Rock Band and Guitar Hero are starting to get stale, and have gone into the DLC and small addon mode, releasing small packs of new content to their current games to keep people playing.
Burnout series is starting to take a turn for the worse as well, had some good games to start but now are just kinda mediocre.
Halo, yes I'm bringing it up, was pretty overhyped even with number 2, I mean it was nice they were working so hard on the multiplayer but the singleplayer was hurting badly in both 2 and 3, and in 3 it seemed a bit rushed like they said, "Ok we have to end this but how?"
FEAR, both 1 and 2 and all the little mini packs in between. They have some pretty simple things and the games work but, I, have to admit, most of the supposed horror was mostly stuff that jumps out at you and makes you jump in your seat a little.
Crysis. Both 1 and Warhead and most likely the new one coming out some time. Crysis was ok when it played smoothly, it even had some hiccups on 360, the gameplay on the first seemed like more of a giant display of the Cryengine, the time between engaging an enemy then moving to the next engagement was atrocious. Warhead was nice and it was what the first one should have been like but still just an ok game.
Right now that's all I can think of, was going to say the GTA series but thought against it, sure 4 isn't the best out of the series but it holds some promise though still pretty shitty how Microsoft said fuck off to the PC version making the DLC packs 'Lost and the Damned' and the new one coming out 'Ballad of Gay Tony' 360 exclusives.