These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternate Character Interpretation: Is Amy really in love with Sonic, or is she trying to hook up with him just so she can be famous too? She always acts like an obsessive fangirl when she's around him, and even he finds it annoying. Plus, Sonic being a hero means he's famous or will be famous someday, and maybe Amy wants to be with him just because then she can claim to be "the legendary Sonic the Hedgehog's girlfriend!"
Any given character has a variety of interpretations. Sonic himself has a few — a few lines from his Sonic Adventure theme song, It Doesn't Matter, could be used to argue that Sonic is less motivated by morals and more by the dangerous thrills his adventures provide. The Sonic Heroes manual mentions that he hates oppression, but does he fight it for the sake of the actual oppressed or does he fight for the sake of his own ego?
Shadow the Hedgehog has as many interpretations as he does songs, including not only the various Shadow the Hedgehog theme songs (I Am specifically questions his moral alignment outright), but the various songs from Sonic Adventure 2 (such as the White Jungle theme, Rhythm and Balance). The franchise has long settled on the heroic All Hail Shadow as his anthem, which still shrouds him in ambiguity. Violent ambiguity.
Archive Panic: Nearly seventy games in twenty years, several animated TV shows, countless cameos in other series, and several comic series, one of which has been around since Sonic's heydey, and is still going to this day.
Base Breaker: Shadow the Hedgehog. The amount of those who consider him at least one of the best things in the series are equal to those who consider him the worst. He was actually quite popular atfirst, but his characterization and unorthodox gameplay from his titular game left many bitter towards him.
Broken Base: Shattered, actually, about every single thing about the franchise. And each faction hates all of the others. This article best sums up the fandom's splintered state. To top it off, Sonic fans are notorious for disliking anything that isn't Sonic—some Sonic discussion forums are practically like a school of piranha, waiting to tear apart anything that isn't Sonic in a matter of minutes regardless of how much merit it has otherwise.
Comedy Ghetto: From Sonic Colors and onwards, some Sonic fans have become absolutely livid with the drastic change in narrative style. Sonic Adventure to Sonic Unleashed featured complicated drama-oriented stories, whereas Sonic Colors to the present has a more sitcom-like comedic approach characterized by minimal plotting and cutscenes dominated by witty dialogue. This is enough for current head writers Ken Pontac and Warren Graff to receive verbal lashings at every fan panel they attend and even death threats over the Internet.
Crazy Awesome: Dr. Robotnik and the Chaotix. Sonic himself sometimes slides into this.
Creator's Pet: Thanks to being a huge Spotlight-Stealing Squad, Shadow the Hedgehog was seen as this in the years following his debut in Sonic Adventure 2, though it has now died down due to not only Shadow, but all of the side characters not having any playable appearances since Unleashed.
Fang the Sniper known as Nack the Weasel in the U.S. a recurring character in the Sonic franchise between the years of 1994 and 1998 has many fans who want him to make an appearance in anything. Some of these fans got their wish when he cameoed on a wanted poster in Sonic Generations.
For that matter Mighty the Armadillo and Ray the Squirrel also got to appear on posters in Sonic Generations and are popular thanks to the Archie comics even though they only appear in the games (SegaSonic the Hedgehog and Knuckles Chaotix).
All of the Chaotix are this, especially after Sonic Heroes revamped them into a trio of screwball, Crazy Awesome detectives. Espio especially. After all, he is a no-nonsenseninja and the Only Sane Man of the trio.
Though they are controversial characters among the fanbase due to appearing in the imfamous Sonic 2006 Silver the Hedgehog and Mephiles the Dark have their share of fans. Silver, after his boss fight in Sonic Generations proved to be actually fun and also do to the Archie comics featuring his as a major character. Mephiles who while his plans are so ridiculously complex that they should not work, fans actually consider him a pretty cool villain. This could be attributed to actually killing Sonic.
Tiara has her fair share of fame despite never being properly released. Tiara's game (Sonic X-Treme) was infamously canceled.
In addition you'll often find a strong fanbase of particular alternate media characters, many of which urging for them to appear in the games canon. Princess Sally Acorn has perhaps one of the most notable fanbases even compared to some games characters (even if it extends to Base Breaker status) with Cosmo and Bunnie Rabbot also worth special mentioning.
A notable classic flame war kickstarter between fans is debating whether the "real" name of the series villain is "Robotnik" or "Eggman". This stems from the US games and tie-ins giving him the dub name of Dr. Ivo Robotnik, until the Sonic Adventure games permanently adopted the Japanese continuity to the western Sonic games, which prompted the characters to start calling him Eggman and start phasing out calling him Robotnik, since Eggman was always his name in Japan, and it was also to avoid the confusion of having two canon names for the series villain at once. Sega eventually settled the issuenote both names are official; Robotnik is his real name, while "Eggman" is the nickname that everyone uses instead, but even this works as well as Shigeru Miyamoto's word on Shiek's gender. It got notorious enough to where the series itself tried to curb this in-canon; the finale of Sonic Generations out and out confirmed that Robotnik is still his real name (in the US version, at least), but the villain himself (fittingly enough his younger counterpart)lampshades this when Young Tails calls him his real name, which prompts him to respond "Nobody calls me that anymore." But this had the unintended effect of adding more fuel to the fire, since many older fans just want him to be called Robotnik on a regular basis again.
Debating the merits of the series voice actors is also shaky territory, but for a while the subject of the 4kids Sonic X actors abruptly replacing the previous voice cast of the games circa Shadow the Hedgehog was a huge hot button for the fan base, and even mentioning the name of actors like Jason Griffith would get fans riled up. Curiously, this eventually simmered down in recent years, due in part to a third voice cast change getting mixed but positive reception, and that fans have moved on, accepting that not only is the original cast never coming back, but that it's pointless or flat-out impossible to get many of them back—Ryan Drummond, Sonic's original actor, runs a talent union now, which currently precludes any chance of him reauditioning for the Sonic role note He was actually offered the chance to reaudition for the role in Sonic Generations, but had to turn it down due to his aforementioned new job , Tails' and Knuckles constantly changed actors in the first place (and in Tails case, all three of them were prepubescent boys who would be much too old to be able to voice him now), Eggman, Gamma and Omega's original actors have passed away, and Jon St. Jon wants nothing to do with Big the Cat anymore and deliberately forgot how to do his voice. Some of the voice actors, even before the third cast change, were even warmed up to, such as Mike Pollock, who has been considered the definitive voice of Eggman and even stayed on the series after the second cast change, and even the disparaged Jason Griffith was ironically noted to have improved his acting as Sonic before leaving the role.
Debating the quality of the cartoon adaptations and tie-in materials to the series (especially in regards to series like Sonic X and its dub) are also rocky territory. Not even the generally well-liked Satam is safe in some circles.
Debating the limits of Sonic's speed (such as whether he can naturally run as fast as the speed of light) as about as risky as asking whether The Flash is faster than Superman. And don't ever insinuate that any other character can run as fast or faster than Sonic.
Just about any mention of My Little Pony: Friendship Is Magic around the fanbase, due to the two fandoms having an intense rivalry with each other. The flame wars between the Bronies and the Sonic fandom almost went nuclear when news came out that Dave Polsky, who writes for Friendship Is Magic, is the head writer of Sonic Boom. And as for the cartoon itself, liking Knuckles' bulked-up redesign can get you labeled as a non-fan/troll.
Calling Shadow's Super Form "Hyper Shadow", a common mistake stemming from Prima's Sonic Adventure 2 game guide. This one is a surefire way to light the fuse to a Flame War. Likewise, referring to Super Tails and Super Knuckles as the less distinguishable Turbo Tails and Hyper Knuckles, which are names that originate from the Archie comics.
Mentioning any of the old backstory used in English speaking countries prior to Sonic Adventure (i.e. Mobius, Sonic's speed coming from his sneakers) and you'll likely be blasted by a group of "Only the Japanese stuff counts" purists. Which will then trigger a war with the "It's our childhood memories and we don't care if it's not really canon" fans.
Not to mention confusing the Archie and Fleetway comics or the six cartoon continuities with the canon of the games.
Debating over whether Sonic the Hedgehog (2006) is really canon, and Crisis City's appearance in Sonic Generations only added more fuel to the flames. Debating over the games quality is another hot button to this day.
A minor one, but confusing Metal Sonic with Mecha Sonic can annoy some fans note Specifically, the two are similar but completely seperate robots, but it's an understandably easy mistake to make and forgive, since this isn't necessarily made clear in the games themselves, only in supplemental material.
Calling Amy Rose "Amy the Hedgehog" or Tails "Tails the Fox" (both are among the few characters to have "real" names in the series, with Tails' real name being "Miles Prower").
Taking any shots at the franchise not matter how big or small, will cause fans to become very defensive. This also includes mentioning the infamous "Sonic Cycle" to fans.
Fanon Discontinuity: Besides some fans pretending games like Sonic 2006 didn't happen, there are a subset of Sonic fans who only consider the classic era games canon, and consider anything from Sonic Adventure and onward non-canon.
Fandom Rivalry: Sonic and Mario were this from the 90's and early 2000's; one of the most classic examples in gaming history. However, fans of both series from that era seem to laugh about the rivalry nowadays and have evolved to become amicable with each other. Newer fans who didn't grow up during that era tend to overlap. There is also a Vocal Minority who grew up during the Console Wars between Nintendo and SEGA and never grew out of it who loathe Nintendo with every fiber of their being for having so-called won the war (as Nintendo continues to make game systems), and they want nothing less than to demote Nintendo to a 3rd-party developer like SEGA, if not destroy Nintendo as a company outright. Where the other Sonic fans were happy to see Sonic get into a Super Smash Bros. game, these fans were insulted to a new degree, as it was undeniable proof that SEGA and Nintendo are buddy-buddy with each other, or they interpreted it as admission of SEGA's defeat due to Sonic being the only SEGA representative in a roster full of Nintendo characters.
Sonic fans and My Little Pony: Friendship Is Magic fans are notorious for clashing with each other, which happens a lot on each other's fansites. This is mainly because the two fandoms are Not So Different, but absolutely hate that fact being brought up. It got so bad that for a while, the famous brony website Equestria Daily explicitly banned any Sonic related content from being posted on it. The rivalries escalated even further when it was revealed one of the writers for Sonic Boom is Dave Polsky, who is a writer for Friendship is Magic.
Fanfic Fuel: The series very lax, open ended direction on introducing new content and elements in each game has made it into a fanfiction gold mine. Not to mention, having numerous incarnations of the series, with alternate timelines and dimensions in the main series alone (and sometimes these continuities even overlap or outright crossover together in content), truckloads of both developed and oneshot characters, a combo of magic / surreal fantasy and video game tropes, with in and out cycles of generally light but existent continuity, light/dark elements, and stronger stories/ excuse plots and an ever expanding world with new elements and locations coming and going (i.e. alternatives to the Chaos Emeralds like the time stones and Chaos Rings, the existence of aliens in several different Sonic games), the characters minimal to nonexistent backstories (particularly Sonic's) the many crossovers and cameos in other major franchises, including Mario, Mega Man, The Legend of Zelda, Super Smash Bros. and even some of Sega's own franchises (Sonic headlines the Sega All Stars series alone, and the amount of cameos he makes in other Sega works, such as NiGHTS Into Dreams, is staggering), and the numerous number of series memes, have given the franchise more than enough material to sustain one of the most active fanfiction communities around.
Friendly Fandoms: As noted above, the Sonic fandom has ironically become one with the Mario fandom. They're also quite friendly with the Mega Man fandom and people who like one series tends to like the other.
The fandom is also on rather good terms with fans of Batman. This is because the largest quantity of vocal Sonic fans grew up in the early 90's, when Batman got a Darker and Edgier take and thus had substantial audience overlap of kids who were taking in the similarly dark and moody Sonic series from DiC and Archie Comics.
Franchise Original Sin: The Cliche of Sonic (or sometimes his friends) using the Chaos Emeralds exclusively as an Eleventh Hour power up, as well as the cliche of Eggman being upstaged by a Monster of the Week that goes out of his control, that started around the time Sonic Adventure was released and was prominently overused in many of the Sonic games since. The recent games (namely Sonic 4, though oddly not Sonic Generations) have been rectifying this by demoting the Emeralds back to bonus power-ups like before, and making Eggman a more prominent villain again. The newest Sonic series, Sonic Boom, has also hinted that while the Emeralds have a possibility of appearing, they may either be downplayed in importance or currently left out of its plots for now.
Game Breaker: Cream in Sonic Advance 2. Makes the bosses a LOT easier. She's a game breaker again in Sonic Chronicles, where she can provide all but unlimited special move use for everyonenote especially if you give her Ferox, which makes Action Commands automatically succeed, or better yet, actually master her Action Commands so that you can pull them off reliably. She also breaks the game in Sonic Battle, where all of her moves are good or decent at worst. That's saying something. Her slightly below average stats don't change this either.
Also the combination of Knuckles with Tails as your partner in Sonic Advance 3 made most levels a joke, considering their combined aerial abilities.
In Sonic Adventure 2: Battle, there is Amy, Chaos, and Tails' alternate costume for the racing, treasure hunting, and shooting modes respectivley.
Amy: She may be slow and can't jump high, but she gets her specials every 10 rings rather than 20. Its not uncommon for her to continuously kill you and freeze you into submission.
Chaos: He's also slow, but he can breathe underwater and his third special freezes the opponent for a whopping 30 seconds!
Alt Costume Tails: No specials, but he moves at speeds that would make Sonic blush!
Gateway Series: Next to Mario, Sonic is definitely one of the first big video game franchises gamers get drawn into, due to its colorful artwork, fantasy tone and casual based gameplay. And by proxy, Sonic is also a gateway to Sega's other big series as well.
Americans Hate Tingle: While not being exactly hate per se, the whole franchise is not very popular in Latin America, barring Mexico (in less degree, thanks to the animated series) and Brazil. Unlike other examples of this, this is not because because Latin American fans hate the franchise or the characters themselves, but because, as Sega's consoles were never popular in that region,note excluding Brazil as it was the only country of that region when the Sega brand was well known the whole series doesn't have the same exposition in that region in the same way Sonic had in the English-speaking world and Europe. For beginners, the Sonic's comics were never translated in Spanish or Portuguese and the whole franchise is only known thanks to the animated adaptations, as the videogames were pretty obscure, compared with Nintendo's characters like Mario and company.note This is NOT an exclusive problem with the Sonic the Hedgehog's games, as all Sega's franchises and games suffers of this in Latin America.
Goddamned Bats: Nearly every single enemy in the second half of Sonic Chronicles can act as this due to either ridiculous defenses, regenerating health, poisoning you every chance they get, leeching off your health, or any combination of the previously mentioned.
The Raptor Hawks in the first half of the game probably count, too. Although there's only six of them at the most, they have 120HP, do ~50 damage per hit, and can use "Evading" whenever they want. It's a good thing when they use their Special move, Feather Barrage, because it's easy to counter.
The artificial chaos enemies from Sonic Adventure 2. Very impressive reach, very hard to kill, and start appearing in levels that are already difficult to begin with!
Guide Dang It: Act 2 of the Carnival Night Zone from Sonic 3 still haunts people to this day.
And sometimes they're all the same "fans".
Hilarious in Hindsight: All of the vintage US Sega ads touting Sonic as the anti-Mario are this now, in light of the fact that Sega is now making games for Nintendo's consoles, and their own mascot has shared a few crossover games with his former rival now.
A Japanese commercial for the original game features Sonic destroying an ersatz Death Star with Eggman's face on it. Fast forward to thesequels, and a Death Star ersatz, the Death Egg, would prominently appear.
There once existed a very long running, polish socialist newspaper called Robotnik. Coincidentally, the third and final iteration of the paper ended around 1990, less than a year before Sonic and Dr. Robotnik made their debut.
In the Sonic The Hedgehog Promo Comic, Dr. Kintobor is busy searching for the seventh Chaos Emerald, having already found the other sixth. Thing was, this comic was written around the time the first game was made, which only had six Chaos Emeralds—the seventh Emerald wouldn't become canon until Sonic the Hedgehog 2.
In Sonic CD, one of the songs sampled in the japanese boss music is Xavier's "Work That Sucker to Death". One of the boss fights in the game involves you trying to outrun a giant treadmill, which grinds away at Eggman's platform in front of you as it gets faster and faster, eventually wearing it out and making it explode. In other words, you really do "work that sucker to death!"
Some fans have noted with irony that the lyrics of the Sonic CD song "Sonic Boom" describe Rainbow Dash more than Sonic himself! And not to mention that "Sonic Boom" became the title of the newest Sonic cartoon Sonic Boom.
The obscure Knuckles Chaotix would have not only a teamwork concept, but Metal Sonic performing a One-Winged Angel, predating their more prominent use in Sonic Heroes by many years. To top it off, both games feature the Chaotix characters.
On that note, Tails Skypatrol features a level called Rail Canyon, which would become the name of an (unrelated) level in Sonic Heroes.
For its original release, Sonic the Fighters (A.K.A. Sonic Championship) saw a limited release in American arcades because Sega of America's executives found the cartoonish slapstick "too violent" and that it would tarnish Sonic's image. Nine years later, Shadow got his own spin-off game, and it was far more violent and intense than Fighters, and another less cartoonish fighting game with the characters, Sonic Battle, was released, and yet Sega of America heavily promoted them. And also, Sonic Riders had lots of cartoonish slapstick just like Fighters, and So A were fine with that too. Also, Fang the Sniper/Nack the Weasel was actually going to use a sniper rifle, but Sega wouldn't allow realistic firearms in the series. Later 3D Sonic games had no problem with using realistic firearms.
One pic from "Sonic The Screensaver" has Sonic finding a magic lamp and using it to wish for a Sega Stadium. Fast forward to 2006, and Sonic would really find a magic lamp (and ring) in "Sonic and the Secret Rings".
Sonic Lost World has a startling amount of similarities to the cancelled Sonic Xtreme in terms of game design, which the developers admitted was a coincidence, but welcomed the comparisons anyway.
There existed a Xbox Sonic skateboarding game that never got past the beta stages called Sonic Extreme. Just a few years later, they'd rework the board racing concept, albeit with a more futuristic flair, into the Sonic Riders series.
Hype Backlash: The series suffers a great deal from this. Ever since Sonic Heroes or all the way up to Sonic Colors, every new game that is announced is met with almost instant approval by fans once more info comes out, only for the game to be nowhere near as good as its hype would entail. The fallout from this is almost a never pretty sight as it leads to arguments about if the game was actually good or not.
Oddly, this isn't really the case, so much as it is a case of Neverlive It Down. The "green eyes" debate was caused by about five members of Sonic Retro during the time Sonic 4 was being hyped, who decided to complain about how the game was going to be horrible and nothing like the classics before going into a rage about Sonic having green eyes. Despite this only being a few select members, this sparked lots of hate towards the (Already infamous) Sonic fanbase, and had people all over the internet claiming that Sonic fans can't be pleased and will complain about anything. This has even become somewhat of a meme among the Sonic fanbase.
When the movie was announced, fans expressed distaste over the decision to make it a CGI/live-action hybrid and not a CGI movie outright.
Just Here for Godzilla: Most fans play the 3D games for the Sonic gameplay rather than for the many, many other gameplay styles, even when it can comprise as little as 1/4th the length of the entire game. This has resulted in Sonic being the only playable character in most of the more recent games (Unleashed and Sonic 4, and Generations if you discount the sidequests).
Many people played the Adventure titles solely for the Chao Gardens. Curiously, this feature was removed from later games despite their popularity.
In games where you collect Chaos Emeralds as part of 100% Completion rather than as Plot Coupons, the classic "got an Emerald" sound is this.
The gasping sound made upon touching an air-replenishing bubble, especially if you were on the brink of drowning.
My Real Daddy: In terms of voice actors, Mike Pollock seems to be becoming this for Robotnik; he's played the character more than anyone else and is the current official voice for nearly every work of Sonic fiction. Not to mention most of Robotnik's other voice actors are either uninterested (Jim Cummings, Gary Chalk) or dead (Long John Baldry, Deem Bristow).
In terms of the development of the games, the series was created by 3 people: Yuji Naka, the founder and former head of Sonic Team, as well as the programmer of the Sega GenesisPlatform Games, Naoto Oshima, the actual creator and designer of both Sonic and Eggman, and Hirokazu Yasuhara, the designer of the very first game's levels (including the famous Green Hill Zone). Similar to Kenji Inafune's involvement with Mega Man, Yuji Naka took most of the credit for creating the series. Sadly, all 3 of them no longer work with Sega, and the series is currently headed by Takashi Iizuka.
Narm Charm: The corny dubs of most of the games may be annoying, but the thrill of the gameplay is usually worth it.
Never Live It Down: Games like Sonic 06 and Shadow The Hedgehog are black marks on the franchise that no one will let Sega live down, regardless of how many good games there are. On a larger scale, the series and fandom will likely never escape the Broken BaseFan Dumb and Hate Dumb that plague it to this day or the reputation gained from said Fan Dumb.
Older Than They Think: A good number of fans seem to think that Amy has only been around since the Sonic Adventure days/is a recent addition. She has actually been around for about or (at least) almost as long as Tails (depending on whether you count the manga or Sonic CD as her debut).
Vector was created around Sonic 1 development, and Charmy is from the same manga Amy made her debut.
The Tails Doll is a bizarre example; it's only appearance was in Sonic R as a Joke Character, and it had no personality whatsoever, being a floating ragdoll slapped together by Eggman. But due to the infamous "Sonic R curse", the harmless looking doll is commonly interpreted as an Eldritch Abomination.
The Scrappy: Take your pick; every medium has one. The main ones from the games are Big (mainly hated by fans for his lethargic, unorthodox gameplay style and one-dimensional characterization in the first Sonic Adventure; even his original voice actor, Jon St. Jon, said he hated the character so much, that he deliberately forgot how to do his voice), Princess Elise, and Exposition Fairy Omochao.
Damsel Scrappy: Princess Elise was kidnapped five times throughout the entirety of the game. The excuse that it was mostly Silver's fault doesn't change the fact that you constantly have to rescue her again and again.
When Silver got a starring role in the Milestone CelebrationSonic '06 with Sonic and Shadow, fans felt he was usurping worthier characters like Tails or Knuckles and accused Sega of being biased against their non-hedgehog characters. His cameo in Brawl also led to claims of this.
Silver being That One Boss supreme in the game didn't help matters, either.
The Rivals games were more enjoyable before we found out Nega kicked Eggman out of the villain spotlight.
Sonic the Hedgehog (2006) managed to make Shadow the Hedgehog more bearable for some of his previous haters. Since the previous game saw him reach the end of his Quest for Identity and resolve to put the past behind him, this game saw Shadow greatly cut down on the angsting and replace it with stoic badassery. And from a purely technical perspective, his gameplay is probably the least broken out of the three main heroes.
In Sonic Generations, even haters of Silver have admitted to loving his new, more powerful form and the boss battle against him. His appearances in the comic have also made him one of Sonic Archie's most popular new characters, to the point of him getting a new Sonic Special.
Seinfeld Is Unfunny: The older entries evoke this in two ways: firstly, the speed which the eponymous Blue Blur ran through the levels in the first game in the series really seemed quite blistering to gamers of the day, even if nobody would think twice about it now, especially in light of the jaw dropping speeds Sonic reaches in later games like Sonic Unleashed and Sonic Generations (the latter compounding this by showing that the younger Sonic is canonically slower than the older one, if just mildly). Also, in order to truly see the heavily promoted "edginess" of the character, which has worn dry over time due to familiarity and Sonic's numerous imitators, you really need to be aware that when Sonic first appeared in 1991, the vast majority of platform heroes were promoted as squeaky-clean and cutesy. A teenage hedgehog with a spiky hairstyle and a self-confident smirk was enough to seem uber-cool by comparison.
Shipping: As with any long running series, there is an (un)healthy dose of this.
Ship Tease: The series isn't really about romance(No matter what the fans try to convince you otherwise) but that doesn't stop it from teasing potential pairings. At least all of the list couples above have been teased at some point.
Die for Our Ship: Let's just say the community isn't very kind to a third wheel in their potential pairing and leave it at that.
Ship-to-Ship Combat: Its Sonamy vs. Shadamy, Knouge vs. Shadouge, Silvaze vs. Sonaze, and Sonaze vs. Sonamy.
It's made all the more confusing because neither of them is particularly interested in romance (bar Sonic X and the comics), to the point where Tails outright hates romance in Adventures of Sonic the Hedgehog, and, to a lesser extent, the games.
So Bad, It's Good: Among the usual candidates named for this are multiple song lyrics, most strikingly We Can, My Sweet Passion, and the in-level Knuckles raps from Sonic Adventure 2, the campy dialogue during levels, and, to a lesser extent, in some cutscenes, and almost everything about Shadow the Hedgehog and Sonic the Hedgehog (2006).
Many Knuckles fans have felt this way, as he started out as a very promising character only for his role in the games to gradually diminish after Sonic Adventure. He suffered neglect through the series' 'character over-saturation era' to the current 'Sonic (and occasionally Tails)-centric era'.
Vanilla Protagonist: Sonic's role in most of the game's plots is to generally be The Hero who saves the day; while he does have a fairly charismatic personality, he remains static for most of the series. It's the supporting cast that get most of the Character Development and more fleshed out personalities, most of which bounces off of Sonic himself.
This also extends to gameplay, primarily in the 2D titles; Sonic tends to be simplest character in terms of abilities while it's the likes of Tails, Knuckles, and Amy who get all of the variations of his gameplay style.
Villain Decay: Reverse-proportional to Eggman's Character Development. As he becomes more and more humanized and sympathetic, he becomes less and less evil. Of course, Eggman has many fans precisely because of this morality shift, so perhaps it isn't all bad...
He's been getting more dangerous as of recent games (Chronicles, Generations). Interestingly this is done without compromising much of his clownish semi likeable personality from before.
What an Idiot: The Nocturnus tried to conquer the ancient world and they did conquer the Twilight Cage — and given the Cage's Year Inside, Hour Outside effect, Shade probably took part in both conquests. Why did she not expect Ix to actually want to conquer Earth?
This is even played up in one episode of the TV series — when a rival genius' shapeshifting robot defects, Dr. Robotnik boasts that he deliberately designed Scratch and Grounder to be idiots, so they'd never defect.
Shadow the Hedgehog was purposefully intended for older fans. It was originally going to have a T rating, but backlash for giving Shadow his own game and intentionally making a Darker and Edgier installment (despite fans requesting that Shadow get his own game since Sonic Adventure 2/Sonic Heroes and requesting for a Darker and Edgier installment for a while) led to SEGA/Sonic Team censoring it to fit for the E10 rating. This shift led to the final product being torn between which group of fans it was trying to appeal to, succeeding at neither.
The inclusion of E102 Gamma in Sonic Adventure, Tails' and Eggmans' mech sections in Sonic Adventure 2, and Shadow's weapon of choice in Shadow the Hedgehog were intended to appeal to a segment of Sonic fans who had apparently been demanding gunplay in Sonic titles. While Gamma and the Sonic Adventure 2 mech sections were average at best, the inclusion of guns in Shadow's game lead to the single biggest complaint people have about the title. Make of that what you will.
The Woobie: E-102 Gamma. First major character to be killed off, after a lifespan of one day, which unlike Shadow or Emerl, was not commemorated or recognized by the other heroes. He shares this with Chip.