Pokemon. It's not that "I'M TOO OLD FOR POKEMON IT'S UNCOOL" kind of phase. I genuinely don't like
it. 8( Feel free to kill me now! I can see the appeal in it, and I can see why it's so popular. But the fandom (and myself, as well) really ruined my enjoyment of the games. It's like all of the magicalness is taken out. All of it.
I haven't played many games that I really don't like, hmm. I do remember trying out Fire Emblem and being pretty bored by it (medieval/classical fantasy things aren't really my thing *shrug*), but I didn't get very far, so I can't say I hated it or anything...