Chico And The Man: Raul (Gabriel Melgar), the 14-year-old "chico." Necessitated after the death of Freddie Prinze, the actor who played Chico, in 1977 ... and for NBC to continue a series that was still doing relatively well.
Some say this happened on Whose Line Is It Anyway? when Drew Carey replaced Clive Anderson as host. Of course, others say this is a subversion. It depends on which side of the Broken Base you're on. The 2013 revival has Aisha Tyler replacing Drew Carey, and now we have a whole new Broken Base over whether Aisha is a terrible host & they should bring Drew back or whether they should have never brought in Drew in the first place.
Mystery Science Theater 3000: Many viewers who prefer the original host Joel over his replacement, Mike, have this trope as their reasoning. This is how some fans of Dr. Clayton Forrester and TV's Frank feel about Pearl, Bobo, and the Observer.
Game of Thrones: Robb's wife Jeyne Westerling from the books was replaced with Talisa Maegyr in the show, who filled the exact same role yet was a completely different character. The fans of the books were generally a little less than pleased with this change. Fortunately for them, her lifespan was much shorter than Jeyne's.
Castle: Captain Roy Montgomery was replaced with Gates, who initially seemed pointlessly hostile towards Castle, behaved abrasively towards everybody, and to many fans seemed more two-dimensional and much less interesting. She got better.
Cheers: When Shelley Long left the show at the end of the Fifth Season—and, therefore, Diane left Boston—the show brought in Rebecca. The writers made it a point to make Rebecca the exact opposite of Diane in nearly every single way: Self-centered and shallow (where Diane was kindhearted and caring), an obsessive gold-digger (where Diane had rejected her family inheritance to seek her own way), and ultimately, emotionally unstable (where Diane's problem was over-thinking things). (Oh, and Rebecca was brunette and voluptuous as opposed to the blonde and slender Diane.) Fan reaction was pretty icy, at first—until the writers stopped trying to make her an Ice QueenStraight Man to Sam and more of a Nervous WreckButt Monkey (seemingly as though to provide catharsis for the fans of Diane).
Plenty of people have commented on the disappointment and sense of loss felt around a regeneration from one Doctor to another; even though it's basically the same character, the changing actors makes it easy to feel that 'your' Doctor is gone and has been replaced by some interloper instead. Fortunately for the show, for the most part each Doctor has managed to put his own stamp on the show and maintain the fans of the previous Doctor (or at least pick up some new ones). Tom Baker, Peter Davison and Matt Smith in particular all suffered from powerful groups in fandom that hated them for not being Jon Pertwee, Tom Baker and David Tennant respectively. There are letters pages in newspapers from the 1960s in which members of the public express outrage at Patrick Troughton for taking over as the Doctor from the beloved William Hartnell, ruining the show forever; the public outcry over Hartnell's leaving got so extreme that Michael Craze and Anneke Wills (who played the First/Second Doctor's companions Ben and Polly), as a Practical Joke, came to work wearing printed tshirts that read "BRING BACK BILL HARTNELL". Apparently, Patrick Troughton didn't see the funny side and was just hurt by it, making Anneke feel awful.
Practically every new Doctor has gotten this to some degree. Colin Baker took a lot of undeserved blame for the show's dip in production values and story content, plus a much more violent, dark tone (not to mention that outfit). Sylvester McCoy took heat for being too silly (at first), Paul McGann initially got blamed for the Doctor-as-half-human-amnesiac of the film, Christopher Eccleston was deemed an interloper because he wasn't Paul McGann (who never got to have his own series) and David Tennant initially was dismissed by classic viewers due to his age. Peter Capaldi was similarly dissed, but because he was thought too old, rather than too young (the public was now used to a young Doctor). Retrospect has corrected most of these first impressions.
Most of the newspapers in 1975 levelled much abuse at Tom Baker for not being Jon Pertwee, with one critic for The Daily Mail suggesting that by casting a more comical Doctor than Jon Pertwee (which wasn't hard - he is one of the most serious Doctors of the lot) the show was becoming a parody of itself (comparing him to Harpo Marx's character in Horse Feathers), and one critic for The Sun calling him "wet" in comparison to Pertwee (who played his character as an Action Hero). Tom Baker defended himself as best as he could in an interview with the Mail, explaining that he wasn't trying to play the Doctor as a comedy character at all, but as someone who was naturally funny due to his alienness, and that he wanted to be a more flamboyant and pacifistic character than Pertwee, to which the interviewer responded "I hope so!". Consider that this is an actor who has been seriously regarded as the best Doctor ever for almost forty years.
In the "Hidden Hinchcliffe" segment on the "Planet of Evil" DVD, Philip Hinchcliffe (who produced an era often considered to be the highest point of the Classic series) complains that every single time he got an audience report, while Tom Baker's performance was generally praised or criticised for sensible reasons, there would always be a tiny minority who would bash everything he did because 'Jon Pertwee was better'.
In the case of Matt Smith replacing David Tennant, it didn't help that the switch coincided with a change in showrunners, from Russell T. Davies (who was the driving force behind the show's revival) to Steven Moffat, who wrote some of the most acclaimed episodes of his predecessor's era but quickly became criticized for changes in the show's tone and for being more interested in plotting than characterization compared to Davies (the latter, ironically, is sometimes why detractors of Davies praise Moffat). Fairly often arguments over Smith vs. Tennant overlap with Moffat vs. Davies and vice versa.
This goes for the Doctor's companions as well, particularly when one arrives around the same time as another departs. Several times, this is even lampshaded in the show, with the Doctor considering the new companion an inferior replacement for his old one:
"The Time Meddler": Ian and Barbara chose to return to their own time in the previous serial, and the First Doctor spends the story in an uncharacteristically gloomy and morbid mood and fishing for attention from Vicki until the new companion, Steven (a Suspiciously Similar Substitute for Ian), reveals he was stowing away on the TARDIS. The Doctor makes it quite clear that he views Steven as an inferior version of Ian, and takes an immediate dislike to him based on this, picking on him and using him as a focus for all his frustration over losing his friend. He soon warms up to Steven when he gets to know him, though not for a couple of stories.
The Third Doctor complained when the Brigadier assigned Jo to him as a replacement for Liz, initially rejecting her on the grounds that he needed someone 'more like Liz' despite having barely spoken to her. But when he actually tried rejecting her to her face, he couldn't bring himself to go through with it. He's similarly suspicious of Sarah Jane as a replacement for Jo later on.
Even the Tenth Doctor initially seems to consider Martha an inferior replacement for Rose.
The show going on as long as it has and the occasional trial-and-error nature of its writing, this is inverted a few times too. Vicki, Suspiciously Similar Substitute for Susan (so much so that Sydney Newman had even wanted Maureen O'Brien to cut her hair and dye it black to look like Carol Ann Ford) is generally seen as an improvement on Susan due to the writers having a more consistent idea of what they wanted to dowith her, William Hartnell's obvious fondness for the actress, and the fact that making her a friend of the Doctor rather than a relative goes a long way towards making the same basic character archetype work. Romana II was and is way more popular than Romana I - partly due to the shift from a Tall, Dark and SnarkyMeta Guy who got constantly upstaged by the Doctor to a character embracing the Doctor's weird world who often upstaged the Doctor, and partly because of the added frisson of her sexier chemistry with the Doctor.
Downton Abbey Lady Rose arrives as an unsubtle replacement for Lady Sybil, only she's sexier, edgier and more rebellious. Designed to embody the Jazz Age, she became central to more than one storyline while remaining unpopular with fans. Her romance with an African-American jazz musician led to a smattering of Deliberate Values Dissonance mixed with Politically Correct History and some leaning toward him being an Ethnic Scrappy.
Arthur Petrelli from Heroes has a rather nasty backstory behind him. Originally a Posthumous Character, he was very suddenly brought in during Volume Three, revealed to have by far the most broken power in the series yet and personal designs on world domination. Further, the very first episodes introducing him were explicitly devoted to his killing off basically every non-Sylar villain the series had cultivated up to that point. Maury Parkamn, the "Nightmare Man" sold in Season 2 as being worse than Sylar, met his end by Arthur, as did the immensely popular Adam Monroe, widely regarded as theMagnificent Bastard to beat. The thing was, though, Maury and Adam were products of Season 2, which was plagued by a writer's strike. While the writers were on strike, replacements were brought in who built up Maury and Adam. The original writers, upon returning, immediately set out to dismantle the work of their replacements, who they had a major grudge with. Thus, Arthur Petrelli was retooled as a Voldemort-esque Bigger Bad. This didn't quite work the way the Volume 3 writers planned, due to Arthur being a Boring Invincible Villain who regularly slipped into Villain Sue territory.
Also even though she was there first, fans did not take well to Matt getting back with his ex-wife after Daphne died.
Star Trek: The Next Generation had Dr. Beverly Crusher's one-season replacement Dr. Kate Pulaski. A lot of it has to do with the shady circumstances surrounding the brief departure of Gates McFadden, and there's never been a clear reason for why she left and whether it was due to conflict with the producers or not. There was also pushback from the fact that she played a much bigger role in her season than Crusher ever did. The third reason was that she was given an abrasive, intolerant, Fantastic Racist personality in an attempt to make her an Expy of McCoy. Fans didn't bite.
Star Trek: Deep Space Nine had Ezri Dax, replacing Jadzia Dax. While the Dax symbiont was still technically there, the Ezri character was a clearly different woman from Jadzia, and many fans preferred Jadzia.
Of course many other fans, while still liking Jadzia, liked Ezri because she was not simply a clone of Jadzia and in fact completely the opposite, which helps explore the way by which hosts of a Trill symbiont, while sharing the same memories, are all very different.
It was lampshaded in-show; upon her first appearance, most of the characters in-show treated her as the Scrappy, including Worf, Jadzia's husband.
Seven of Nine. Fans accused the writers of replacing Kes, a likable character with a lot of untapped potential, with a Space Barbie. Some acrimony over how Kes inexplicably turned evil and tried to kill everyone didn't help. Seven was originally supposed to replace Harry Kim, who was basically an Advertised Extra at that point (notice how Kim is grievously injured in the episode we first meet Seven). However, this was vetoed by the executives after Kim's actor was named one of the sexiest men on television. And so Kim got better, and Kes was Put on a Bus several episodes later.
Eventually Seven of Nine turned out to be a fan favorite, because of her interesting character, and Jeri Ryan can act. Seven and The Doctor became the Spotlight-Stealing Squad of the show. On set, however, it had been reported that the rest of the cast treated Ryan as the Replacement Scrappy, and despite their great on-screen chemistry, Kate Mulgrew (Captain Janeway) was alleged to be particularly harsh towards Ryan due to her close friendship with Jennifer Lien (Kes) as well as perceived spotlight stealing as Ms. Fanservice.
When Chappelle's Show ended prematurely after Dave's Creator Breakdown, Comedy Central quickly filled his time slot with Mind of Mencia, another show anchored by a comedian specializing in racial humor. On the first episode Mencia even tries to reject the label of being "A Hispanic Dave Chappelle". Chappelle fans sure went ape-shit over this one. It helps that the show was panned by critics and the comedy community on its own (lack of) merits.
Everybody remembers Steve from Blue's Clues, right? So where'd this "Joe" guy come from? It didn't help that the show underwent some major retooling not long after he was cast. Naturally, the actor took the brunt of the backlash despite having nothing to do with, say, live-action puppet sequences.
Jonas Quinn to the point when a massive Internet campaign was organized to bring Daniel Jackson back. The fact that Jonas Quinn had a higher intelligence than most humans, an eidetic memory and very high skills of observation, to the point that he was obviously being brought in as the "upgraded Daniel Jackson" - who conveniently memorized all of Daniel's work and so could fill his role instantly - did not help.
Colonel Cameron Mitchell filled the same job as Jack O'Neill but minus his angst, disdain for science, etc. A well-thought out, unique character, and well-liked character played by a very good Ben Browder. But he was never EVER gonna be Jack O'Neill. Which is why he was a "well-thought-out, unique character" in the first place: because they knew they couldn't replace O'Neill. As such, Mitchell is more an aversion of this trope than a straight example.
There was a bit of a backlash when Dr. Beckett was replaced with Dr. Keller. But because Dr. Keller was Kaylee on Firefly, the hate was restricted to "No offense, Jewel, but..." This is also considerably influenced by the reason Beckett was unavailable; many fans were ambivalent toward or even liked Keller, but just hated the way Beckett was killed off.
Many fans disliked Elizabeth Weir being killed off to make room for Amanda Tapping, as Col. Sam Carter, to hop series when SG1 concluded. Most fans liked Carter — it was, after all, Samantha Carter, one of the most beloved characters in the entire franchise — but felt that killing Weir off was unnecessary and killed the cast chemistry which made Atlantis enjoyable. To add insult to injury, Carter's character was much weaker on Atlantis than she'd been on SG1, as the writers tried to make her fill Weir's role instead of having her be herself. Amanda Tapping only remained on the show one season before leaving to focus on Sanctuary, and was in turn replaced by Robert Picardo, which worked out a little better, but was still not an adequate replacement for what Torri Higginson brought to the show.
In addition to this, Stargate Universe faces this, since it replaced Stargate Atlantis. In the series proper, we have Lt. Matthew Scott who one of the creators said was like "The Jack O'Neill of 10 years ago". Fan consensus promptly countered with the fact that we actually liked Jack O'Neill, 10 years ago and still do.
Tara King (Linda Thorson) replacing Emma Peel (Diana Rigg) - who herself replaced Cathy Gale (Honor Blackman), let us not forget, in The Avengers.
The opinion of the majority of Beakmans World fans who don't like Liza and Phoebe is summed up in the fact that they're not Josie. Especially Phoebe, who gets the double stigma of not being Josie or Liza. That, and the fact that: 1) Phoebe was more of a Jerkass towards Lester than the other two, and 2) Phoebe was more of a smart-ass than the other two.
Lampshaded by Colin Quinn on the first episode in which he replaced Norm MacDonald in the Weekend Update sketches on Saturday Night Live: "You know how you go to your favorite bar, and your local bartender isn't there? You ask, 'Where's Jeff?' 'Jeff no longer works here, I'm Steve.' Then you're thinking, hey, who's this idiot? I like Jeff. But you still want your drink. And even though Steve doesn't mix your drink the same way you're used to, like Jeff, you still like the bar. You don't want to have to go to a different bar. And even Steve might feel kinda bad because Jeff trained him. Jeff showed him how to work the cash register, where the tonic was on the soda gun, who tips, who doesn't. Well, I'm Steve. What can I get you?" Although he was not considered a replacement scrappy, he still was not very popular and didn't last long in the position before being replaced himself.
Kennedy was both the Replacement for and the Antithesis of Tara. Tara was quiet and shy, helped ease Willow more into the world of magic, showed genuine love for Willow, and was accepted as a member of the Scoobies in her own right eventually. Kennedy, in contrast, was direct, blunt (not in an endearing Anya-like fashion), insulted the idea of magic to Willow's face, and basically come on to Willow very strongly simply because she managed to recognize her as a fellow lesbian, with the relationship having pretty much zero buildup and the two characters having nothing in common apart from a mutual friend in Buffy. You can see why the fanbase reacted so violently to her, especially as Tara's replacement only several months (in-story) after her death, which caused Willow to go on a murderous rampage.
Wesley joined the cast right after Doyle died. Doyle's popularity with fans, combined with the fact that fans weren't exactly eager for Wesley to come back, led to some serious anti-Wesley backlash. There was even a border-line lamp-shading moment where Wesley is called by Doyle's name accidentally and everyone suddenly feels very awkward. By the end of the season, however, he was generally accepted by fans and characters alike.
Spike's abrupt inclusion into the main cast, clearly a replacement for the similarly blunt Cordelia, was met with strong reactions with many of the longtime fans. After the overwhelmingly negative reception for the storyline that put Cordelia in the coma (that led to her exclusion from the main billing), many saw this as the last nail in the coffin for the series, fearing that Spike had only been brought in so that his fans would come over from Buffy and that all the plots would end up being about him. This, however, wasn't a general consensus among fans, as some enjoyed Spike's role in the series, and the worst fears of him taking over the show weren't realised.
Also on Angel, in season five the simpering Eve replaced the vastly superior Lilah, to much dismay from the fans. She was quickly replaced by Marcus Hamilton, who made no attempt to act as an ersatz-Lilah. Cordelia lampshades this trope in "You're Welcome", referring to Eve as "Lilah Jr."
Remote Control had a fan backlash (mild— this was pre-Blog) when the first hostess, Marisol, was replaced first with Kari Wuhrer and then by a string of lesser lights.
In-story, one of the most cringe-inducing part of the Mexican telenovelaCarrusel was when a bunch of third-graders hostilized their sweet, clever and well-intentioned new teacher for just replacing their Team Mom of a teacher. It was very petty from them, VERY badly-acted, and the old janitor of the school, usually the gentlest person in the world, bitched the brats out for treating the poor girl like crap.
Richard Roeper as Roger Ebert's partner in film critiquing, following the tragic death of Gene Siskel. Ebert even softened the blow by bringing on a variety of guest hosts before finally sticking with Roeper, but people still missed Siskel and Ebert's legendary chemistry.
When Ebert & Roeper was retooled into At the Movies in 2008, now hosted by Ben Mankiewicz and Ben Lyons, the response from longtime viewers quickly escalated into Hatedom. Lyons became the subject of mockery at Efilmcritic.com's "Ben Lyons Quote of the Week", and even Roger Ebert himself called him out for his poor work, not naming him but quoting his reviews from the show — arguably Lyons qualified as an actual Scrappy. A year later, they were dropped and replaced by Michael Phillips and A.O. Scott (from Chicago Tribune and New York Times, respectively).
Bailey was this for Maddie in The Suite Life of Zack and Cody. While Maddie was very smart and nice, she still had a ton of flaws. For example, where she excelled academically, she failed physically (often failing gym). She was a good student, but thanks to London, Maddie's homeroom teacher thought bitter of her. Maddie was very sarcastic, has shown on various occasions that she is easy to bribe with money and although smart, wasn't nearly as accelerated as Cody. Baily, on the other hand, is basically a Mary Sue. She rivals Cody in academics, and unlike Cody's ex, Barbara, she wasn't prone to jealousy, nor was she a priss. All of the teachers and staff loved her, she was physically fit, and was too moral to fall for bribes. Needless to say, she's next to Woody and Marcus as the least favorite characters of the entire franchise.
Edward Tudor-Pole replacing Richard O'Brien as the presenter of The Crystal Maze.
Dexter Fletcher replacing Dominik Diamond for one series on Games Master.
Oliver (Richard Mylan) replacing Jeff on Coupling when Richard Coyle would not return for a fourth series.
El Chavo del ocho did this numerous times, rather temporary or definetive replacements:
Don Ramón has been replaced by Don Román in 1975 and by Jaimito el Cartero in 1979/1980 and 1982-1990.
Doña Clodtilde was replaced by Doña Eduviges for two episodes in 1973.
But the most unpopular is Malicha, who replaced La Chilindrina (when actress María Antonieta de las Nieves was pregnant), she had the same personality of Chilindrina and they were both related to Don Ramón (Chilindrina is his daughter and Malicha, his goddaughter), but she wasn't Chilindrina and was cut out after three episodes and was never ever mentioned again.
The numerous changes on Are You Being Served? resulted in a few Replacement Scrappy cases. Many fans despise Mr. Grainger's first replacement, Mr. Tebbs, even though cast members and numerous other fans have said that he did a brilliant job. More serious was Mr. Spooner's replacement of popular Mr. Lucas after the seventh series, though in the fans' defense, Mr. Spooner's personality was never developed beyond rudeness. Even more-hated was Old Mr. Grace for Young Mr. Grace, which was justifiable since it was tackily executed by pasting a middle-aged actor with loads of old-age makeup.
Rose on Keeping Up Appearances being portrayed by Shirley Stelfox in Series 1, then Mary Millar in all subsequent series (though this might actually be an improvement...)
Dads Army replaced the character of Walker with Private Cheeseman after the sudden death of James Beck, who played Walker. Cheeseman became unpopular both with viewers and fellow cast members (John Laurie is on record as saying that he felt both the character and actor were fast approaching Spotlight-Stealing Squad status) and was written out at the start of the next series.
Robin Hood introduced the character of Kate in the third series, to replace the departed Marian and Djaq. Before a single episode featuring her had aired, she was being criticised in the fandom as a poor replacement and a Canon Sue; pre-publicity material frequently described her as "feisty" and hinted that she would become Robin's new love interest. The first episode she appears in was duly broadcast, and the same fans said "See, we were right."
And let's face it, any original female character who is brought in for the sole purpose of replacing the legendary Maid Marian as Robin Hood's love interest is doomed to be despised for the crime of not being Marian. Why did the writers even try? It may well be the only case in which hating a character for being a replacement is totally justified.
Randy from That '70s Show was supposed to be a replacement for Eric - he even dated his longtime girlfriend, Donna, after they broke up inexplicably and offscreen. Practically every fan hated him. The writers finally caught on to this; he barely appears in the finale. Even worse, they started trying to make him a replacement Kelso as well as a replacement Eric, despite the fact that the two characters were vastly different. This resulted in Randy being a dumb nerd, a socially awkward player, and an unfunny clown.
The X-Files: Agent John Doggett, and later Agent Monica Reyes. Doggett has his share of fans, but Reyes... not so much. Doggett was written into the show for its eighth season as an agent who was put on a task force to look for missing Agent Mulder. Agent Reyes was added as a regular in Season 9 to pair up with Doggett. They didn't have a chance to be loved as much as Mulder and Scully were.
A series of Replacement Scrappies, most notably Lee Meriwether as Tracy, filled in on Mission: Impossible after Barbara Bain left. Lesley Warren eventually got the role of Dana for the fifth season, and was treated as a Replacement Scrappy by some. Others found her replacement, Lynda Day George, to be more Scrappy-ish.
"Secret Agent Spock" (Paris, to give him his real name) replaced Martin Landau's Rollin Hand (and technically both Paris and Dana were replaced by Casey, since she was also the team's disguise expert).
A clean-shaven (!) Sam Elliott was brought in as Dr. Doug Robert for Season 5, replacing Willy Armitage (Peter Lupus). Fan reaction was so negative that the doctor was let go, and Willy was brought back.
Diane Neal as Casey Novak on Law & Order: Special Victims Unit, replacing Stephanie March's beloved Alex Cabot, actually averted this. The fanbase generally warmed to Novak — she's easily the second most-popular ADA the show has ever had (and the longest lasting), with reactions that amount to "We really do like you, Casey, but we want half of our OTP back" — but then she was Put on a Bus and replaced by Kim Greylek (Michaela McManus), who was so despised that the producers got rid of her before a full season was even up. (They brought back March. There was much rejoicing, particularly from the large section of the fandom who loved the Alex/Olivia Les Yay.)
Law & Order has had their share of cast replacements over the years, but most have been handled pretty well. Among the more notable Replacement Scrappies are Nora Lewin (Dianne Wiest) for Adam Schiff (Steven Hill), Joe Fontana (Dennis Farina) for Lennie Briscoe (Jerry Orbach), and Serena Southerlyn (Elisabeth Rohm) for Abbie Carmichael (Angie Harmon).
Briscoe himself is a pretty notable aversion of this trope; having replaced Phil Ceretta (Paul Sorvino) who himself replaced Max Greevey (George Dzundza), Briscoe went on to become one of the show's most popular characters and a pretty iconic example of a TV cop in his own right.
Sam Casey for Matt Devlin on Law & Order: UK. The sad thing is, he wasn't a bad character or actor at all, he just simply wasn't Matt. He and Ronnie lacked the rapport and chemistry that the previous pairing had had—and was arguably the most enjoyable part of the show—and a few of his dumb moves didn't do him any favors either. His replacement, however, Joe Hawkins, seemed to avert this.
Kate Barker for Alesha Philips, also on Law & Order: UK. Her first appearance, as the defense attorney for a man responsible for the death of numerous people as well as some of her dumb moves didn't endear her to the viewers either. As well, she appeared to be based on one of the less popular ADAs from the original series, Serena Southerlyn, a Replacement Scrappy herself.
Nickelodeon's Salute Your Shorts swapped out Michael for Pinsky in its second season, and fan opinion appears to be fairly evenly divided as to whether he was a more outgoing and fun personality or an obnoxious loudmouth with the aggravating tendency to get portrayed as The Ace.
Babylon 5's Elizabeth Lochley was doomed to be disliked, as she was the replacement for the widely beloved Susan Ivanova. Combined with her former relationship with Sheridan and the fact that Season 5 is considered the show's weakest, she couldn't really avoid it.
Another Nickelodeon/Game Show example: Ben Lyons (again) and Australian celebrity Asha Kuerten replaced Mike O'Malley and Moira "Mo" Quirk, respectively, in My Family's Got GUTS. While Asha was praised by some fans for equalling Moira, fans pretty much preferred Mike and Moira/Mo, even though they weren't employed by Nickelodeon at the time and were working on other projects.
Many people believe that Langston was a replacement for Grissom, since Langston showed up right after Grissom left. However, while Catherine moved up to fill Grissom's spot in the unit's hierarchy, and Langston was starting at the bottom, he was still heavily promoted as the new "face" of the show and was assigned responsibilities more befitting a shift administrator like Grissom despite being a rookie. It probably didn't help that a lot of people watched the show and thought "Why is Morpheus on CSI?"
In the third season of Mutant X, many fans hated Lexa when she was brought in to replace Emma. The let down of Emma taking a level in badass at the end of season two, only to be killed off screen in the first episode of season three didn't help.
Head of the Class had replaced a bunch of students in its fourth season. Maria, Jawaharlal and Janice were replaced by Viki, Alex, Aristotle and TJ. In it's fifth season, Mr. Moore the teacher played by Howard Hessman was replaced by Billy MacGregor played by Billy Connolly.
Earth: Final Conflict replaced a character every season. At the beginning of the second season, Boone was replaced with Liam, and then Renee replaced Lili, Street replaced Augur, and in the last season, Renee replaced Liam, becoming both the lead and the female. The show suffered each time.
In the third season of Red Dwarf, the actor playing Holly was replaced with an actress playing Holly. The in-show explanation was that Holly got a face-sex change. The new Holly was never as funny or pleasant to watch as the old Holly, and the show began to feature Holly less and less.
This was less to do with the change of actor, more that the third series introduced Kryten, who was a more suitable character to provide the plot exposition previously provided by Holly. Word of God is also that they got a new producer who didn't really know how to do the Holly scenes (pointing a camera at Hol's screen, rather than feeding the Holly image in directly.)
Additionally, Kochanski in one of the later seasons replaced Rimmer. Apart from the fact that she replaced the best character in the show, Kochanski herself wasn't funny or interesting at all.
House losing his entire team at the end of Season 3, and eventually bringing in three new doctors. Thirteen got the worst of it by far.
While Thirteen's never really recovered from it, Taub and Kutner did move out of Replacement Scrappy territory fairly quickly, thanks to Taub having a dry sense of humor that could rival House's at times, and Kutner being a loveable dork. What helped their cases was that they basically had half a season of introduction before becoming official team members thanks to House's "auditions."
Then the show took this Up to Eleven in Seasons 7 and 8 by getting Replacement Scrappies for the first Replacement Scrappies. The addition of Masters, Adams, and Park solidified the show's Seasonal Rot, and the network decided that the eighth season would be the last.
Tory Foster in Battlestar Galactica was regarded as this after she replaced Billy who got killed in a terrorist attack.
There are several shades to the story, though: Part of the reason why Tory was considered a scrappy was because Billy was seen as a very nice guy and a son figure for Roslin. On the other hand, some people took a liking for Tory precisely because she seemed cold and ruthless. So, she could have gone both ways. Unfortunately, bad writing and the lack of Character Development ruined her. She got barely any exposition on her darker motivations, her relationship with the rest of the Final Five or her past.
Fantasy Island had this problem; in the final season they replaced the famous Tattoo with the forgettable Lawrence.
Blue Heelers made the shocking move at the beginning of the seventh season to kill off the much beloved Maggie, and knowing they couldn't hope to match her popularity, the writers didn't try to. Instead, her replacement was the standoffish Tess, who lasted four seasons before Flanderization set in and she was written out for Susie.
Aside from that the show generally did well in averting the Replacement Scrappy. After Wayne's death he was replaced by Dash and was an instant success. Then when she left Jo came in as a popular character. Ditto Jack after Adam left. Those who disliked the character however very much cheered his replacement, Jonesy.
Power Rangers Turbo is a weird variant, as the season is considered one of the weakest in the franchise and one of the cited reasons is that they replaced nearly the entire cast over the course of it (Rocky, Zordon, and Alpha 5 with Justin, Dimitria, and Alpha 6 at the beginning; the other four Rangers midseason). However, most individual characters, while not as fondly remembered as their longtime predecessors, are considered mostly inoffensive - in fact, the second half of the season gets a better rep than the first, and the latter replacements continued on into the highly regarded Power Rangers in Space. Not too shabby for replacements.
That said, a couple of the new guys are thought of as Scrappies; but on their own merits and not just because they replaced the old guy. Justin was half the other Rangers' age and bumped up to high school to be with them, thereby reeking of being the Kid-Appeal Character and Creator's Pet. Dimitria came from a Planet of Hats whose shtick was Figure It Out Yourself (though she dropped this when the latter replacements came in). Alpha 6 was a Jive Turkey and ruder than 5 was; traits which were thankfully removed in the carryover to In Space.
Going back to the first three seasons of MMPR, the Replacement Rangers were not well liked initially. Rocky (for Jason), Adam (for Zack), Aisha (for Trini), and Kat (for Kimberly) were all met with some venom, but most were able to get past it. Poor Kat got the worst of it, since Die for Our Ship was also at play for the Tommy/Kimberly fans.
Jo Danville from CSI: NY has gained some hate for replacing popular character Stella and being seen as "flirting" with Mac Taylor.
Degrassi has a bit of this due to a refocus of the show. As a Long Runner set in a High School they had to either move up to college episodes or lose the older members of the cast... they eventually decided on the latter dropping most of the old cast and bringing in a bunch of new young cast members. Between Season 8 being a very weak season and the loss of so many fan favorites, the new cast was not taken well. Most have grown into their own but several never got past this and were dropped from the show. Blue and Leia being the poster children for this issue.
Americas Funniest Home Videos went through this when Bob Saget was replaced with John Fugelsang in 1998 and an assistant, Daisy Fuentes, was added for little more than eye candy. Most fans of the series consider the Fugelsang era the show's nadir. The show then limped along for a while as a "special" set of episodes with rotating hosts, before current host Tom Bergon joined in 2001 and the show became watchable again.
Pretty much every character in Homicide Life On The Street who was introduced later than about the fifth or sixth season. Especially Falsone, Ballard and Sheppard, who are often dismissed as being purely there as fanservice for respectively female and male viewers.
Dr. Billy Peele as a replacement for Dr. Matt Crower in American Gothic. The showrunners have since gone on record that this was down to Executive Meddling by people at the network who believed that Matt wasn't a "strong, heroic" (i.e. macho asshole) antagonist for Lucas, Completely Missing the Point that the main conflict was over Caleb's moral development rather than any specific situation and that the kindly, gentle Matt was meant to be a demonstration that you can't fight moral corruption with aggression. This led to a spectacularly malicious plot towards the end of the show where Billy was led to believe that he was bringing Selena to a High Heel-Face Turn only to discover that she was setting him up as a patsy for Lucas's murder. When even the writers make it clear that they think you're a Scrappy...
When a bitter Kate Jackson left after the third season of the popular female detectives show Charlie's Angels, the producers scrambled for a replacement for everybody's favorite "Smart Angel". Enter Shelley Hack, who for many Angels viewers practically defines the trope in every sense of the word. Hack portrayed the glamorous Tiffany Welles, a cop from Boston who spoke Latin, and was always fashionable. Unfortunately, Hack wasn't given much to do during her tenure on the fourth season of Charlie's Angels, simply because the writers could not seem to come up with anything for her to do, and as such, she was scarcely seen doing anything of note during the season. Because of this, Cheryl Ladd's character Kris Munroe was given the brunt of most of the storylines, with the occasional Kelly Garrett (Jaclyn Smith) story thrown in, particularly in the season finale. Viewership sank as a result, and Hack was widely blamed for the ratings drop, even though she herself had nothing to do with it, it was in actuality the writers whom were to blame. Hack was immediately fired from the show, and the character of Tiffany Welles was sent back to Boston. Hack's replacement for the fifth and final season was Tanya Roberts as street smart model Julie Rodgers. Though Roberts was received well by critics, she wasn't enough to save the show from cancellation.
Rossi started out as one in Criminal Minds, but got better. However, JJ's replacement Ashley Seaver plays this out painfully straight.
When Leverage brought on Tara to replace Sophie in season two (due to Gina Bellman's pregnancy) she became this for many fans. Her insistence on being paid also irritated viewers who didn't like how it contrasted the charitable actions of the main cast. Some sections of fandom still hate her, while others warmed to the character and came to enjoy her as a temporary team member.
Her insistence on getting paid is only fair. The rest of the team made countless millions in their first job, she obviously didn't as she wasn't around. It is somewhat hypocritical for the main team to criticize her on that issue.
Ben Mankiewicz has managed to be the replacement scrappy on no less than three different projects: replacing Roger Ebert and Richard Roeper on At The Movies, subbing for Cenk on The Young Turks and taking over afternoon introductions for Robert Osborne (while Osborne still does evenings) on Turner Classic Movies. The general opinion of all three happens to be that he's not as good as the originals.
At the beginning of Season 5 of Becker, Reggie (played by Terry Farrell) suddenly left and the diner was taken over by Chris (Nancy Travis).
Jool from Farscape. Partly this was a deliberate ploy by the writers: the much-loved Zhaan had been killed off because the actor fell ill, and they decided to create a new character who would roughly fill the same "brainy female character" niche but be completely different in almost every way, including being abrasive rather than kindly and lovable. Some people never warmed up to her as much as the writers hoped, though, to say the least.
Max Louis in season 5 of NewsRadio. After Phil Hartman's untimely death, Jon Lovitz joined the show to replace his departed friend for what turned out to be, not coincidently, the show's final season.
The sci-fi teens show The Tribe had tribeleader and main character Amber replaced by Danni after Amber's death at the end of season 1. While Amber already had Mary Sue tendencies, what with being the Leader and uncountable guys attracted to her and all, but Danni was just downright unbearable. She got Amber's boyfriend and went from total stranger to tribeleader in half a season, which made not only Amber-Fans hate her guts. Luckily, after we find out Amber was never dead at all, she is quickly re-replaced, never to be seen again. None of the other characters seem to mind much.
Paige from Charmed is a notable aversion. True she was brought onto the show to replace Prue but she was fleshed out into a completely different character than Prue and is quite popular among fans. Most people who say they prefer the episodes with Prue and dislike the later seasons don't have a problem with Paige herself but rather the difference in tone.
Dan from season 2 is a straight example. Fans didn't take to the attempt to replace Leo with him and he was dropped after one season.
Ziva on NCIS started out as this. With all the outrage over Kate's death, the news that Ziva, who not only wasn't Kate, but was the half-sister of the terrorist who killed Kate, was going to be her replacement was not well received. Proving herself a couple of times in season three, most significantly by killing Ari and helping Gibbs recover his memory, she managed to redeem herself in the eyes of the fandom.
Taylor Townsend was seen as this for Marissa on The O.C. despite being introduced before Marissa was killed off. Marissa's sister Kaitlyn could also be seen as this.
Inverted with How It's Made host and pro swimmer Mark Tewskbury. He was the show's first host, and also the most hated, mainly because he did absolutely nothing to fight the common stereotype that all athletes have very dull personalities and voices. Predictably, many people skip the parts where he introduces the show, and hate the fact that they're forced to listen to him drone on during the narration.
Rudy from Misfits is this to many fans, after being introduced in season 3 as fan-favourite Nathan's replacement, and some have boycotted the series in protest. In fairness, it's hardly the show's fault the actor playing Nathan decided to quit, but so far the most common criticism aimed at Rudy is that he is fartoo similar to Nathan in terms of personality, but too wangsty and not as funny. On the other hand, some fans like him, leading to a bit of a Broken Base situation.
It gets worse in season 4. After Kelly is Put on a Bus and Simon and Alisha are trapped in a time loop, the three are replaced by Jess, Finn, and Alex, who have yet to show any trait they didn't borrow from the original characters. Finn has both Simon's timidity and Nathan depraved humor, while Jess has Kelly's tough attitude and Alysha's sarcasm. However, watching them makes you only miss more and more the original cast.
Walden Schmidt on Two and a Half Men is seen by many as a poor replacement for Charlie, mainly because Ashton Kutcher's comedy style just doesn't seem to fit in with the show, and his interaction with the other characters feels rather forced and unnatural.
Sliders went through quite a few cast changes, the most infamous of which was the replacement of Jerry O'Connell with Robert Floyd. This was sort of a hybrid between The Other Darrin and an outright replacement: Floyd's character was ostensibly an alternate-dimension double of O'Connell's character, Quinn Mallory. (Why he looked, acted and sounded absolutely nothing like his "double" is Hand Waved with a Techno Babble explanation in his first episode.)
This happens whenever a new lead character shows up on Primeval. After Nick Cutter died, there were fans who didn't approve of Danny Quinn. Matt Anderson got a simlar treatment, though that wasn't to do with replacing Danny, but more the fact that many people found him bland.
Averted with Captain Becker. Even though many fans were sad when Steven Hart died, Becker quickly became a popular character in the fandom.
At about the same time Anthony Head as King Uther left Merlin, Nathaniel Parker was introduced as Arthur's uncle Agravaine (there was only a three episode overlap between the two characters). Though different in many ways, he was essentially a male family member who provided guidance and advice to Arthur (albeit treacherous advice). For a number of reasons, he didn't go down well with fans, one of them certainly because he was unfavourably compared to Uther, having not nearly as much development or complexity as his predecessor.
24 introduced quite a few within season seven. For the first, CTU was decommissioned in between seasons six and seven with the FBI office taking the agency's place as the main government group that Jack worked with to stop the threat of the Day. Only problem? The FBI did really little to actually establish itself as being that different from CTU and outside Renee Walker the agents themselves weren't particularly memorable, leading fan reaction to be pretty poor. CTU was then brought back into the picture for the final season. For the second, the entire season prior had been building up Jonas Hodges as the main villain, and introduced him halfway through it. Thanks in particular to Jon Voight's incredibly hammy yet charismatic performance, Hodges quickly became well received, but only six episodes later his plot was foiled and he was removed from action while the real season 7 villain Alan Wilson revealed himself. As opposed to Hodges, Wilson had little-to-no personality, the fact that he was introduced so late into the season didn't help matters and the attempt to make him more of a credible threat by revealing he was also the real mastermind behind all of the fifth season's events near the end was more controversial than anything else.
A recurring trend now for Downton Abbey despite still having a large cast as it is.
Lovable and ambitious housemaid Gwen left to become a secretary she was replaced in the second season/series by arrogant and unprofessional Ethel. Ethel eventually did get something of a storyline that took her out of the Abbey (YMMV if her character improved from it).
Alfred replaced Thomas as the ambitious footman since Thomas leaves his position, but later returns as Lord Grantham's valet.
Jimmy replaced William as the second footman in the third series. His storyline is mostly involved with Thomas.
Cousin Rose joined the cast to fill the rebellious young woman void after Sybil's death, but so far lacks the charm and compassion that Sybil had.
Ivy, a maid, joined after Daisy was promoted to assistant cook. She doesn't have much of a personality aside from being a flirt.
Halfway through the seventh season of Supernatural, Bobby Singer, hunter coordinator, the Winchester boy's father figure and a recurring character since the first season finale, was killed off to make the current Big Bad seem more threatening. Around the same time we were introduced to Frank Devereaux, a Hollywood Hacker who served basically the same role on the show except he was more paranoid. He also made Dean ditch his iconic 67 Impala on the grounds that it was too recognizable, which was probably true, but at the same time had never been an issue in the past seven seasons. Needless to say fans didn't take to Frank and he was also killed off before the end of the season. His replacement, Garth Fitzgerald, has been somewhat more popular, though it probably helps that Garth had been previously established on the show before Bobby was killed off, is a wildly different character instead of a Suspiciously Similar Substitute, and is only used sparingly rather than shoehorned into the main plot.
Gale Boetticher is an In-Universe example on Breaking Bad: He's extremely nice and intelligent, but Walt can't control or abuse him in the same way that he could with Jesse. Ultimately, Walt decides to fire Gale so that he can get Jesse back.
Larry King and Larry King Live being replaced by Piers Morgan and Piers Morgan Tonight on CNN. Larry King Live was the television interview program, running since 1985, which was a continuation of Larry King's radio program which ran since 1978. There was no way CNN could find a replacement that could live up to that legacy when they did not bother to renew King's contract in 2010, but going with the already controversial Piers Morgan was not a great choice (his show was axed after a mere three years).
Happened in the fourth season of Glee with "New" New Directions. After half of the original kids graduated at the end of Season 3, five new students were introduced. However, none of them caught on with viewers as much as the originals, mostly because they filled the same roles as the kids who left: Marley was literally declared "The New Rachel", Jake was Puck's younger brother, Ryder was Finn in all but name, Kitty idolized Quinn, and Unique even described herself as the lovechild of Kurt and Mercedes (it didn't help that the new kids even looked like the ones they were copying). Some argue that due to Glee having Loads and Loads of Characters by this point, the new kids never had a chance to shine. Others were simply more interested in the grads who moved to New York City. Eventually the show dropped the Lima-based characters altogether to move the story to New York full time.
With Scarlett en route to being redeemed on Nashville due to a) her drug use and b) having a mother who makes Juliette's late mom seem like Olivia Walton, and fan non-favourite Teddy also not completely despised, Scarlett's Black Best Friend and tedious storyline regular Zoey fills the vacant spot. Luke "Wheels Up" Wheeler is also not beloved by viewers, not least because he gets in the way of Fan-Preferred Couple Rayna and Deacon.
Lindsey Butterfield was designed as a deliberate Suspiciously Similar Substitute for Lynsey Nolan; who shone in the serial killer storyline with Silas Blissett, but was then murdered by Dr Browning in a copycat killing. Lindsey has the same name (albeit spelt differently), same job, and very similar looks to Lynsey; which drives Browning to a breakdown as he believes her to be Lynsey's ghost. Since the end of that storyline, Lindsey has mostly been caught up in standard Love Triangle drama, and many fans find her very dull compared to her predecessor.
After the death of popular villainess Clare Devine, her sister Grace Black was introduced to the show. She was quickly lambasted by viewers for being annoying, supposedly not as attractive as Clare, and being part of the none too popular gangster storyline. When Grace was told in-universe that she should have died instead of Clare, very few fans disagreed.
The House of Anubis fandom was not too pleased with either Willow or KT, who seemed to be replacing Amber and Nina, respectively. While some still see them as this, things have calmed down once the characters settled into their unique new roles and proved to be not so much like Nina and Amber as people thought they'd be.
Subverted on Dr. Quinn, Medicine Woman, when Sully's friend Daniel came to town to help search for the missing Sully. Originally, the plan was for Sully to be Killed Off for Real (his portrayer, Joe Lando, wanted to leave the series to take on new projects and spend more time with his family) and Daniel to be Mike's new love interest. Distraught fans flooded producers with a "Save Our Sully" campaign and the decision was amended—although Daniel still became the show's new male protagonist, Sully was kept alive (but with reduced screen time to accomodate Joe Lando's wishes), thus mostly avoiding any vitriol.
Arrow has a unique case where the Replacement Scrappy was introduced before the preferred character. Laurel was a major civilian character in Season 1 and her sister Sara appeared as a masked vigilante The Canary in Season 2. Come Season 3 Sara is killed and Laurel is taking over her vigilante position as The Canary. However since Sara was hugely popular as The Canary with a complex backstory while Laurel is endlessly criticized for her poor characterization and has virtually no training, the change....hasn't gone well. Essentially they've managed to upgrade The Scrappy to Replacement Scrappy.