Note: This article lists examples which take place within fandoms, mostly involving over-reaction about minor changes. It's not about the opinion of TV Tropes as to whether a change is for the worse. TV Tropes doesn't have opinions.
This is the opinion the head writers and editors at DC (led by Dan Didio and Geoff Johns) had about the changes their predecessors made to the DCU in the 80s and 90s, in particular Crisis on Infinite Earths and Emerald Twilight. As a result, Infinite Crisis, Green Lantern Rebirth and the multiple Batman/Superman crossover events have been their way of retconning those changes, leading to backlash from the current ifandom shouting that the current changes have ruined the DCU FOREVER.
The DCNU relaunch is already getting "They changed it now it sucks" backlash.
As noted by coverage at the San Diego Comic Con, this is mostly due to bad advertising where the main blurbs are "see, we're going back to how it used to be" (aggravating current fans, who weren't reading when it was how it used to be) and not giving out details people actually wanted that weren't very spoiler-oriented (Was Tim Drake still Robin in his past? What happens to Stephanie Brown? Did you really just say Ma and Pa Kent are both dead? Does Wally West exist at all? Why does this feel all Elseworlds-ish?? Etc.)
Changes to Batgirl gets a lot of this. Barbara Gordon being crippled was this. Barbara Gordon being uncrippled was this. Barbara Gordon being uncrippled compounded with the Asian Batgirl and the Batgirl from a lower-class background being erased was this and Unfortunate Implications.
There was some controversy surrounding the decision to retcon Cyborg into being a founding member of the Justice League, with some fans angered by what they saw as mucking around with the team's history for the sake of diversity. So far though, the new Justice League title has been the highest-seller of the reboot. It's not clear yet what happened to post-crisis/pre-flashpoint Huntress and Power Girl (they either got merged with the new ones or wiped from history). But the prospect of losing the characters they knew only to get back the (pre-crisis) characters only the writers remember doesn't sit too well with some current fans.
Wonder Woman's new revamp initially to be got this reaction, the general consensus being that the coolest thing about it would be watching the fan's reactions. The first two issues were met with massive acclaim and were extremely strong sellers though. It's been said that it successfully got readers not normally interested in Wonder Woman to check it out. One change in particular that upset many fans was the fact that Diana is apparently Zeus's daughter.
The announcement of slimming up the full-figured Amanda Waller resulted in a lot of fans crying foul as they consider her figure to be an integral part of her charm. ("Her nickname's 'The Wall'. That's not a wall, that's a fencepost.") Like other characters post-New 52, Waller also found herself significantly de-aged, which also earned criticisms as the original Amanda Waller was a middle-aged widow with grown children.
James Robinson's run on Justice League of America got this reaction, mainly because of his decision to focus on seven second-stringers: Batman (Dick Grayson), Donna Troy, Jesse Quick, Jade, Supergirl, Starman, and Congorilla, rather than on the "real" Justice League (defined by those who complain as either all A-Listers or as whichever team they grew up reading about). Robinson himself is aware of it, and has made it known that he considers this league as "real" as any other, yet this has done little to stop the sheer amount of complaining on DC's official boards. There was some griping about the Unfortunate Implications behind Robinson getting rid of all the non-white characters like Vixen and Doctor Light in order to write a group of his mostly-white pet characters. Lampshaded in the final issue, where Batman makes a very thinly-veiled speech about not caring about how poorly his version of the League was received by the public, and that they should be proud of their team.
Some fans of the Ultimate Marvel line of comics are pretty clear about their opinion of the new Ultimate Comics line : because it takes place after Ultimatum and as a result of it, all the stories in it are complete garbage and the people who likes it are bribed/tasteless/morons.
To put it into perspective, before Bendis took over, the Avengers were barely selling well enough to maintain one title. By the time his run ended, the franchise was popular enough to support no less than three different titles (Avengers, New Avengers, and Secret Avengers).
Batman Reborn and Superman: New Krypton, two events released around the same time, garnered similar responses, at least initially. Superman was pulled out of Superman and Action Comics, with those books being taken over by Mon-El, and Nightwing and Flamebird respectively, while Damian Wayne was made into the new Robin, Dick Grayson into the new Batman, and Stephanie Brown into the new Batgirl. The flagship title Detective Comics was also given to Batwoman. While Batman Reborn proved to be a massive success, New Krypton was met with almost-universal critical panning and falling sales. The New Krypton event was eventually Cut Short, and Superman was brought back to his namesake series.
A general strong reaction by readers of American Flagg after Howard Chaykin left the book. Neither Steven Grant nor J.M. DeMatteis could meet fan expectations for the title, and even an (admittedly gonzo) storyline written by Alan Moore was poorly received.
One More Day: A very large proportion of the Spiderman fandom declared the storyline as its collective Berserk Button, after Joe Quesada considered dealing with Marvel's answer to Satan (who has since tacitly confirmed that he is Satan) a more realistic way to break up the much loved Spider Marriage than oh, divorce, or something like that. Due to this, the large amount of Executive Meddling and the Mary Sue new love interest for Peter in the form of Carlie Cooper, it went down like a lead balloon.
The ending to Amazing Spider-Man #700, which has Peter Parker dying in Dr. Octopus' body and Dr. Octopus taking over as the new Superior Spider-Man in Peter's body, been met with this reaction after it was leaked two weeks before the issue hit the stands. Many who were interested in it before have either decided to abandon it or try to send death threats to Dan Slott. Numbers are set to drop even further with the apparent end of the Hope Spot in Superior Spider-Man #9, criticisms including the plot mandated Idiot Ball handling of the Avengers and X-Men, and not noticing a full blown psychic possession in a universe chock full of powerful telepaths.
The main issue with Malibu's attempt at a Street Fightercomic. They took so many liberties with the franchise's canon that Capcomliterally stepped in and asked them to stop publishing it.