Silent Hill - Played 2 first, and well... SH just wasn't as good as its sequel.
MGS3 - I know everyone says its the best one, but I just don't see it. It's the only one I didn't finish, including the PSP games.
Dragon Age: Origins - I just don't have that kind of time anymore
Fallout 3 - Ditto
FF XII - just didn't like it
Mario 64 - I played Mario Galaxy first, and it was really hard to take that step back in control conventions, graphics, and sound
Ocarina of Time - Same as above, but with Twilight Princess
Battlefield: Bad Company 2 - I just don't like it. The mechanics, the story, any of the characters.
Army of Two - Sold it back after beating one level.
No More Heroes 2 - The third form of the last boss can suck one. I breezed through the entire game, and now it's gonna make me work for it? No. Screw you. You are a Wii game. I'm going to go play something fun, challenging, and devoid of an undeserved smug sense of self-satisfaction. You are not as cool as your predecessor.
Crackdown - I just don't see this game's appeal. Maybe because I played Prototype and InFamous first.
and finally...
Dead Rising - I know it's supposed to be difficult, but there's a fine line between "high difficulty level" and "broken mechanics with punitive save function".