When the license for Marvel Comics toys went from ToyBiz to Hasbro, fans declared that the toys were Ruined FOREVER. Some even sold off their entire collections in "protest." The fact that Hasbro's first series of Marvel Legends had been designed and created by the ToyBiz crew, and would in fact have been ToyBiz's next series if the licensed hadn't transferred, didn't seem to matter to these folks. The only change was the name printed on the card, and that was enough.
LEGO has its fanatics, especially when it comes to its "Constraction" lines, like BIONICLE. Never mind the Fan Hater crew, even the line's followers expressed their hatred over several "drastic" changes. Some felt the story went downhill when the characters started speaking (as in, the very first page of the very first comic). Others left the story when the setting changed from a tropical island to a futuristic city. Then, when the marketing took a sharp turn and advertised the sets with horrible rap songs and (decidedly non-canon) websites, even more fans turned away. And then there was The Reveal of the Great Spirit, the introduction of a new planet, and the sudden overflow of sci-fi elements. Thankfully, in contrast to many other fandoms described here, BIONICLE's fans never declared outright war over the subject. However that still doesn't mean there aren't any seriously butthurt people out there, banned from popular forums.
The dropping of the Bionicle line for the more kid-oriented and multimedia Hero Factory caused many to claim LEGO's death, while in fact they were laughing all the way to the bank.
LEGO is also widely known for how, when you were a kid, it was all about being creative with boxes of generic blocks, whereas now it's all specialized parts designed around building one particular model. This complaint has been around for so long that it's begun actively disproving itself—after all, if a man born in 1992 misses the sets from when he was a kid because they allowed for so much creativity, then clearly the man who complained in 1997 about how LEGO sets didn't allow for any creativity anymore must have been off the mark a bit.
Professional Wrestling figures, every time the style of figure changes or a different company starts producing them. Even if said figure series provides far more articulation, more realistic face scans and less chance of breaking than a previous series, people won't be happy. The best example is from Bone Crunching Action to Titan Tron Live - Bone Crunching Action had barely any articulation, were made of rubber and looked ugly. Titan Tron Live had much articulation (more as the series went on) and soon the faces looked much better, but they were criticised by the Fan Dumb who didn't want to start their collections all over again.