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.
Happened in the BIONICLE fandom every time the characters received a redesign. Notable offenders are the Toa Inika and the Toa Nuva's "Mistika" forms. Perhaps the biggest "unacceptable" change of the franchise was when the tribal island setting of the '01-'03 lines got replaced with a futuristic mega-city, and the storyline drifted away from epic fantasy into light-science fiction territory. Unlike most other examples, almost all of these shifts were in fact planned ahead in the official Universe Bible, and hints were dropped all the way through — however the First Installment Wins, and any "change" is by default regarded as evil by casual fans who haven't been actively following the toys' and story's advancements. Some extremists even complained about changes that LEGO had no control over, such as all the characters that had to be renamed due to legal reasons.
Greg Farshtey: This is BZ Power, and all new sets are greeted with a barrage of criticism. It's tradition.
Surprisingly heavy fan-backlash happened when, concurrently with the '04 story shift, LEGO introduced the infamous "blay" color, gray colored pieces with a somewhat bluish tint, just about entirely replacing the earlier normal dark-gray color.
Every change that happens in the Fashionistas line is met with criticism and complaining.
Quite a few people don't like how Polly Pockets don't exactly live up to their name anymore.
They still fit in your pocket but now it is just the doll that fits inside your pocket instead of their whole world.
Sometime fans of earlier generations of My Little Pony will complain about the new generations.
Beyblades, specifically the Engine Gear system. But not looking into it's parts separately.
The price of small-scale Lego sets have dramatically increased, but so many consider it corporate suicide.
Transformers action figures, post-2005 and beyond, were lambasted for what are minor imperfections and frailties. After the ultra-complicated and realistic robot designs of the live-action films resulted in some huge advancements in the way the toys are constructed and how their transformations work, there have been numerous complaints that they are simply too tough to transform now (with the complainers seemingly being oblivious to all the sub-lines whose figures still offer the same level of complexity as pre-Movie Era toys). A bunch of superficial design details, like the broken-up panels, insect-like faces and "chicken legs" also make many fans angry. Though in all fairness, in the case of a handful of figures, it is difficult to decipher whether the designers intended them to fit in with the Classics-line or Movie-line toys.
Inverted. The exact opposite is now happening with the Transformers Prime line. After the initial, poorly-distributed "First Edition" assortment showed off what seemed like highly complex, innovative, and accurate transformation, it was abruptly canceled in favour of the mainstream "Robots in Disguise" line, which were slightly simplified, had "kiddier" gimmicks and weapons, and relied a bit more on "fake" kibble. Many fans of the earlier figures were outraged, believing that the new figures suffered from "forced simplicity" being thrust upon them for the sake of younger kids (which, as one would do well to remember, are still the true intended audience for the figures, adult collectors being merely a Periphery Demographic). Never mind the fact that quite a few of them are actually not really worse than their predecessors in terms of quality and functionality; rather, they simply attempted things differently. It hasn't stopped fans from declaring the whole line ruined as a result.
The 2002 revival of G.I. Joe action figures got considerable backlash for removing the "O-ring"note A black rubber-band ring that connects the upper body of a G.I. Joe figure to the lower waist area. and replacing it with a "T-bar", limiting the figures' familiar articulation.
Most people who liked K'nex for being a clever offshoot of Tinker Toys were less than thrilled to see them beginning to use pieces that bear a blatant resemblance to LEGO bricks. Most of this came from those who thought they were being original in the wake of a building toy market filled with knockoff versions of LEGO.