Gears of War 2.
I really wanted to like it. I really did. Then the whole thing just fell apart for me. The campaign isn't nearly as classic as the first one. With Gears 1, I think I've played through that campaign at least five times, and each time was just as much fun as the last. I'm almost done with Gears 2's campaign on Hardcore (first run-through) and I don't know if I can put up with it long enough to finish it. It's just depressing, and it feels like work.
I also expected them to fix the multiplayer, because Gears 1 was a great foundation, and I thought if they fixed some of the lag issues from Gears 1 and left everything else the same, it would've been an amazing experience. But instead there are just more issues, and (IMO) a worse matchmaking system.
It's just depressing how much that game was a letdown to me.
And I've never been much of a GTA guy. Yeah, going on rampages with the all-weapons-cheat was fun for five minutes, but I couldn't sit through the campaigns without using cheat codes or anything. I guess I could never take them seriously.