The Gremlins are a Roald Dahl creation that Disney originally planned to turn into a cartoon. They're more a Looney Toons property at this point, because there was a Looney Toons cartoon featuring the same design of Gremlins, created by Roald Dahl.
The reason why I think it's a bad game? I can pick up Super Mario 64, Banjo-Kazooie, or Banjo-Tooie and have a far more enjoyable experience. In those games, there's more you can do, there's more enemies, and there's more diverse worlds.
In contrast, Epic Mickey has stale platforming due to a lack of Mickey's ability to do anything other than double jump. There's a minor handful of enemies. The combat gets repetitive after a few hours. There's never-ending quests and repeat treks through the same areas. The game holds no candle to many things from fourteen years ago, to put it simple, except in story. If I wanted unclear objectives and dull stage design, if I wanted a boring platformer or a week puzzler, or if I wanted a game void of fun, I'd choose Epic Mickey. The thing about Epic Mickey is that aside from the few bosses, one of which is a rip-off copy from Super Mario Galaxy, is that after the first two hours, you've seen everything there is that's worth seeing, you've done everything there is that's worth doing, and nothing new or interesting happens until the very end.
It's not because it's "Anti-Wii" hate that reviewers dislike the game. Besides, not all reviewers do dislike it. It's that they were expecting compelling stage design, platforming elements that are slightly more complex than just jumping and double-jumping. It's that they were expecting enemy fights that didn't feel like the same thing time and time again. They were expecting a world that didn't feel extremely generic where townspeople say one of a slim number of lines and just ignore you. They were expecting not to have to run through the same worlds a dozen times just to get from point A to point B for a meaningless, filler quest.
So yeah, why do some reviewers dislike it? It's boring, it's repetitive, unoriginal, and it's one-upped by games that came out over a decade before it.