The Honeymooners was a spinoff of The Jackie Gleason Show that didn't fare too well against competing shows. The 39 episodes it managed to air before cancellation are today regarded alongside I Love Lucy as quintessential 1950s television and the foundation of the modern sitcom.
The Addams Family: Not particularly successful in its original run, but a hit in syndication.
The original Star Trek series was canceled after three seasons due to poor ratings. Then the studios started doing demographic studies, and it turned out the show they just cancelled was actually one of their top shows among the best demographics. The show was given loads of syndication reruns, which earned it loads of more fans over the years. Soon there were plans of reviving the series (which became the films), and the rest is history.
On a smaller scale, Star Trek: Deep Space Nine was initially mocked for "not going anywhere" and people tended to watch the more "exciting" spaceship set Star Trek: The Next Generation and Star Trek: Voyager instead... but it's since earned the best critical reviews of any Star Trek series and has become a kind of franchise Ensemble Dark Horse, with more people listing it as their favorite series now than when it aired. This is usually because of the fact that the setting was stationary, letting the creators add more depth and introduce serialized story arcs — common now, but rare at the time.
In universe, the high-warp engine designed by Henry Archer with Cochrane was thought to be a crackpot dream by many. Expanded Universe books reveal that initially, Starfleet, was ready to go with the ion-warpdrive. In the Trekverse, the dilithium chamber warp drive has been the standard going into the 24th century.
Patrick McGoohan's sci-fi classic The Prisoner didn't last long on ITV, with a style so unconventional that the executives in charge were terrified of a second season being made. Some sources say that McGoohan only wanted the show to last 7 episodes, with the network wanting far more (somewhere between 26 or 37), and that they compromised on 17.
Monty Python's Flying Circus was badly received at first; the studio audiences were largely old ladies (hence the use of the Women's Institute Applause Stock Footage) who expected an actual circus and the show was put out at odd hours of the night. It only gradually picked up its cult following.
Space: 1999, although enjoying some popularity at the time (1975-1977) has been a poster boy for poor writing, poor science, poor directing, poor acting. However, most of these criticisms are directed at the very different second season which was produced by Fred Frieberger, a figure noted for ruining good science fiction shows. Despite the handwavium throughout the series, the first season is now remembered as being deep, thoughtful, and metaphysical. Despite a widespread perception of the show favoring special effects over story it can't be denied that the show had visual effects that still hold up even today. Many of its effects crew went on to even bigger things (such as Star Wars and Alien) further cementing Space 1999's place as the show that helped George Lucas and Ridley Scott discover good technical talent.
Fawlty Towers (the first season in particular) was lambasted by British TV critics who didn't find it inspired or funny at all. Gradually it became a cult series and eventually the most popular, critically acclaimed and often repeated British sitcom of all time.
WKRP in Cincinnati was originally an underdog property of MTM Productions (CBS changed the show's time slot a dozen times in four years, leading to its early cancellation), but the syndicated reruns catapulted the series to recognition as one of the greatest TV sitcoms of all time.
During the era of the Seventh Doctor (Sylvester McCoy), Doctor Who received poor ratings and drew much criticism, resulting in it being put on hiatus for 15 years. The second and third seasons of that Doctor's tenure is now widely praised for its gritty realism, complex plotting, and return to a more mysterious portrayal of the Doctor.
Also, Colin Baker - often proclaimed "Worst Doctor Ever!" - has made a great many fans come around with his outstanding performances in the Big Finish audios. Additionally, over time there has become a growing agreement in the idea that Colin Baker himself was not to blame for the show's problems, but rather the quality of the scripts as well as behind-the-scenes difficulties. The infamous rainbow coat on the other hand, is still much-maligned.
While the contemporary criticisms of Season 16 and 17 for being too silly remain agreed upon (although with some grudging admission that it was amazing they got anything on the screen at all with all the strikes, budget problems and lead actor mental health issues), "City of Death" was much hated by the fanbase when it aired for being too farcical and stupid. Nowadays, it's one of the most beloved Classic serials and frequently makes top ten lists. Steven Moffat is a huge fan, and 4chan's perennial Doctor Who discussion thread "/who/" even voted it the best Doctor Who TV story ever.
"Pure historicals", stories set in historical periods with the presence of the TARDIS crew being the only science fiction element and usually dealing with questions like the morality of interfering with history, were considered by contemporary audiences to be dry and boring and got progressively more and more unpopular as the series progressed. Ratings tanked especially hard during "The Gunfighters", the story which all but killed the format. There has always been a minority calling for the return of this format, but today it is generally agreed upon that Hartnell's pure historicals tend to be his best stories. They tend to have rather more mature and witty writing than the show's early attempts at science fiction, don't suffer from Special Effect Failure to the same extent, and have less Early-Installment Weirdness than many of the surrounding stories, despite the fact that being a historical is itself Early-Installment Weirdness. Pure historicals usually cited as amongst Hartnell's best include the rather mythologised Missing Episode "Marco Polo", "The Romans", "The Myth Makers", "The Massacre of Saint Bartholemew's Eve", and "The Aztecs" (often given as a contender for his very best stoey). "The Crusade" and "The Reign of Terror" are less popular, but have more defenders than the contemporarily highly popular sci-fi serials "The Web Planet" and "The Chase". The only pure historical that is generally considered bad is "The Gunfighters", although that's a special case: 1) fan lore held that it was an awful story due to an especially damning write-up in the review book Doctor Who: A Celebration which was around before home video, so fandom took its opinion as gospel (although its loving write up in the later review book The Discontinuity Guide is eroding its reputation), and 2) it's a comedy and to some extent a Musical Episode, so was always going to be a Love It or Hate It story.
"The Deadly Assassin", a Doctor Who storyline with no companions, a focus on alien politics, and with an awful lot of Family-Unfriendly Violence was viewed at the time as a failed experiment at best (the absence of The Watson made the plot much harder to follow than normal, and the execs said it was never to happen again no matter how much Tom Baker insisted that it worked) and tasteless and audience-inappropriate at worst (notoriously attracting so many complaints that the show was Re Tooled into a much less violent, more comedy-based series for most of the rest of Tom Baker's run). Fans nowadays tend to appreciate the attempt at trying something other than Monster of the Week, the more impressionistic and political tone, the especially brutal and exciting action, and in particular the Alternate Character Interpretation that the Doctor gets in the story; due to not having an ally to talk to, he comes off as a brooding, quiet and much more mysterious character with a pinch of Spaghetti Western hero about him, a sharp contrast to his usual funniness and Obfuscating Stupidity. It's not a usual candidate for Tom Baker's best serial (which tends to be given as "City of Death" or "The Talons of Weng-Chiang") but is often listed as a standout, must-see episode and a bit of a hipster favourite.
Police Squad! challenged the attention spans of American viewers in the early 80s. Only 4 episodes initially aired, but a few years later it became a cult phenomenon and inspired its creators Zucker/Abrahams/Zucker to revive it in the feature film The Naked Gun.
The first season of Cheers was the lowest-rated sitcom in 1982. Critical acclaim allowed the show to survive into a second season, which became a smash hit and effectively vindicated season 1.
Anne Beatts — who in the 1970s had teamed with boyfriend/writing-colleague Michael O'Donoghue to bring sadistic edge to the early seasons of SNL — created in 1982 a teen sitcom called Square Pegs. The material presented in Pegs (more adult in nature than the average 12-to-19 demographic offering at the time) resulted in public alienation and ratings disaster. A fandom grew around the show over the course of the decade — enough to propel lead actress Sarah Jessica Parker to stardom.
Twin Peaks, despite heavy promotion and initially glowing reviews, failed to maintain its audience as its content progressed into more and more unusual territory. ABC gave up and cut the cord after the second season, but the show's style continues to influence television drama.
FOX's Space: Above and Beyond debuted to middling ratings and mixed reaction from critics and viewers when it premiered in 1995. The show, which centered around a group of outer-space Marine pilots fighting to stop an invasion by an otherworldly alien force, was roundly criticized at the time for being "Full Metal Jacketin space". It was cancelled at the end of its first season (due to pressure from parents' groups over the violence in the show), and appeared to disappear from the ether... that is, until stations like the Sci-Fi Channel and the Space Channel (in Canada) started airing marathons of the show, and audiences began to watch it in droves. It then picked up a cult following for blazing trails no other sci-fi series had done up to that point: highly serialized plots that relied on minor stories and comments from previous episodes, a realistic treatment of military politics, CGI used as a narrative tool, gender and ethnic diversity, and permanent cast and story changes. It was even ranked in IGN's list of Top 50 Sci-Fi TV Shows. Today, the show is considered to be one of the defining sci-fi series of the 1990s, and helped shape the current wave of serialized sci-fi shows (like Battlestar Galactica).
Premium cable channel HBO has its fair share of belated success stories:
Mr. Show was a show with sensibilities that didn't click with mid-1990s mainstream; its viewership was very small. Sketch comedians Bob Odenkirk and David Cross, who created the series, are now two of the most influential artists in their field, popularizing the brand of comedy found in Mr. Show. The series is a smash hit on DVD.
The Wire spent its five seasons for the most part ignored, a minor-league show overshadowed by the likes of The Sopranos. A while after Wire ended, Barack Obama (a huge fan) became the U.S. president and his public appearances increasingly referenced the show. It is now showing up on numerous critics' lists as one of the greatest television dramas ever made.
Carnivāle had extremely high production values and was honorably daring in its thematic scope, but suffered a disastrous barely-viewed two seasons and as time went on showrunner Daniel Knauf found himself at war with the network. The second season ended on a cliffhanger that was destined never to be resolved; nevertheless the show continues to garner enormous posthumous acclaim.
Deadwood was a series HBO was really proud of, but low ratings versus too high a budget forced them to cancel it after the third season. With heavy promotion in the DVD market, audience acclaim has skyrocketed.
Freaks and Geeks lasted one season and was seemingly forgotten once it was over. The show has since skyrocketed in popularity.
Malcolm in the Middle was initially building up momentum as a must-see sitcom, but because of FOX's constant switching of timeslots and the resulting nuisance in trying to find Malcolm, the series suffered ratings failure. Eventually general disinterest (though there was a small cult fandom) forced the writers to wrap up the show's loose ends and call it quits. Since the show ended, the actor who played the father, Bryan Cranston, went on to star in Breaking Bad, one of the most critically acclaimed dramas of all time. Many people have watched the show to see Bryan. In reruns the series is very popular.
In Survivor, Richard Hatch was hated by the viewers because his approach to the gameplay was seen as unethical. Nowadays, he's considered one of the best players to ever play the game, and aside from a few others like Rob Cesternino, Vecepia, and Cirie, invented most of the strategies commonly used in the show today, and is often considered one of the best people to ever play the game. (Apart from Rob Cesternino, who was actually eliminated because he was Dangerously Genre Savvy.)
Firefly underwent some serious Executive Meddling during its original run that it was cancelled after only 11 episodes managed to air. Today, Firefly as a whole is now hailed as a sci-fi classic.
Arrested Development aired for only three seasons before being cancelled. The show was well received and won six Emmys and a Golden Globe, but it got low ratings which were mostly due to its time slot constantly being switched and its lack of advertising. A year after it was cancelled, Time magazine listed it as one of the best 100 TV shows of all time, and it has since achieved a cult following. There has been talk of an Arrested Development movie ever since the show was cancelled, and most of the cast has expressed a desire to be in said movie.
Fifteen new episodes saw a Netflix release in 2013. Mitch Hurwitz annouced that more Arrested Development would be coming in some form. Netflix has expressed interest in producing more episodes as well.
Veronica Mars impressed critics and a small fandom but never achieved decent ratings in its initial run. CW Network cut the show short when the third season concluded, and for years remained a minor curiosity until fairly recently hitting it big.
Thanks to a Kickstarter campaign by Rob Thomas and Kristen Bell, a feature-film continuation was released in 2014.
Big Brother US - Brendon and Rachel. They managed to score a pretty big hatedom that Rachel was still wangsting about the next year. The next year, they're suddenly considered the best people in the house. The fact that they were aligned with Jeff and Jordan might have helped. As one poster on Jokers put it:
Pushing Daisies got only about one season's worth of episodes in all when it was on during 2007-2009 (due to a writer's strike) but is now recognized as a unique, wonderful tv show by people and Bryan Fuller has confirmed a revival of sorts recently.