Note: This article lists examples which take place within fandoms; not the TV Trope's opinion as to whether a change is for the worse. TV Trope doesn't have opinions. The focus is on over-reaction about minor changes.
The Warrior Cats series gets hit hard by this andIt's the Same, Now It Sucks due to Fan Dumb. The fanbase can't decide whether things should take a totally different route or revert back to what it was like in the first series. It's not that they can't decide so much as they will freely use both tropes depending on what plot development they're talking about.
Ranger Rick (one nature magazine published by the National Wildlife Federation) has had several redesigns due to different artists, and presumably a desire to update with the times. It started out rustic, then became more modern, then simplified for a look more appropriate of a comic book, then made the jump to 3D. The switch from the beautiful modern look of the 80s and 90s to the comic-book look in the early 2000s is a popular choice for when it all went wrong.
Sweet Valley High had a revival of the original series in 2008. They incorporated modern things in the stories like the Internet and cell phones which weren't commonplace when the series began in 1983. They also updated the teen slang and changed a lot of the iconic Sweet Valley landmarks. Many SVH characters received makeovers: most notably, the Wakefield twins shrank to a size 4. The changes didn't attract new readers and it turned off the original fans, prompting the publisher-Random House-to cease publication of the "new" books after book #6.
Scary Stories to Tell in the Dark: They replaced the Stephen Gammell art with new art by Brett Helquist. The books with the original illustrations have been discontinued by their publishers and online prices are being inflated by the negative response to the newer versions.
The 1997 edition of the venerable cookbook The Joy of Cooking received a major revamp supervised partly by the original author (Irma Rombauer)'s grandson. The tone shift (in particular, dropping Rombauer's first-person conversational narration) was disliked by many.
Every time a new Discworld main character is introduced (such as Moist or Tiffany) fans complain that they've taken the spotlight away from the "established" characters such as Commander Vimes and Granny Weatherwax. Sir Terry Pratchett has pointed out that if he'd listened to these people right at the start, he'd have written thirty novels about Rincewind, and there wouldn't be a Vimes or Granny.
Honor Harrington started out as a light space opera mostly focused on naval combat, but over the course of its dozen or so books has morphed into a galaxy-spanning political thriller epic (with plenty of naval combat). Cue the whining from an unhappy portion of the fanbase. Meanwhile, the readers who like the political epic quietly think to themselves, "But... but I like it this way better..." Poor MWW. He just can't win.
In-universe in James Joyce's A Portrait of the Artist as a Young Man. A priest at school tells Stephen Dedalus and some other students that he thought Victor Hugo's work after he broke with the Church to be not half as good (The joke here, which is easily lost today, is that Hugo broke with the Church very early in his career. This is akin to saying that The Beatles went downhill sometime after, say, Beatles For Sale).
A workplace management book about this phenomenon exists called Who Moved My Cheese? about some mice and some "littlepeople" who live in a maze and seek out and find cheese to eat. One group looks for new cheese every time their stash is "moved",note It is implied that the cheese wasn't moved, but that the littlepeople simply ate it all. while the other group just complains. Guess which does better? The implications of the book, as some have noted, is change for change's sake is good. If you leave the cheese in one place, it's easier to find, and the mice don't have to spend time looking for it before they can eat. Other authors wrote unofficial sequels with various aspects of the implications in mind: two titled Who Cut The Cheese?, one Who Stole My Cheese? about the financial scandals of the Turn of the Millennium, and finally I Moved Your Cheese 2011 about how the mice end up controlling those outside the maze.