eh I would say MW2 is certainly up there, the online is sooooooooo unbalanced and glitchy its insane. Also the campaign is super short.

Oh crap, I completely forgot Ninja Gaiden 2. I was super disappointed in that one (was the reason i got a 360 basically at launch), though other NG2 fans convinced me pretty well that my tastes in games changed more than the game being a let down.

Maybe I'm just too picky now, or have too high of standards, as it seems I've been let down a lot. The good news is, I've played more games I absolutley loved in this generation than probably every other generation combined.

How was Gears of War 2 a worse sequel? It was a WAY better single player game than Gears 1.

you beat me to it, well said.

a current list of the games has been added to my OP

As much as i hate to have to say this but i would have to agree with FFXIII and also R2 being the worst so far that i have played. I mean FFXIII is awesome in visuals but the gameplay is waaaay to restrictive and also the lack of towns/airships/actual people that you can interact with makes the game a hell of a lot down on the progress X made in the genre! I mean no controllable airship was my only gripe in that game!

Resident Evil 5, definitely. It wasn't a horrible game, but it certainly was inferior to the 4th one.

NGS2.
I hate the new karma system........

Most Disappointing sequels this gen:-

1- Final Fantsay XIII
2- Grand Theft Auto IV
3- Resident Evil 5
4- Street Fighter IV
5- Ninja Gaiden IV
6- Tekken 6
7- SoulCalibur IV
8- Gears of War 2

Most disappointing, now that's a different beast. I would have to go with MGS4 then, I feel that the story got out of control and overran the dated and lack of gameplay. I did like the game though, but MGS1 is still the best!

Worst has to be Gears 2 most disappointing was RE5 even though overall its still a good game.