Like many others said in this thread Metal Gear Solid 4 takes the cake for me. This was a very disappointing game indeed and not just in 1 area. The story fell apart and left plot holes even after the ending not to mention parts of it were incoherent, I'm all for a complex narrative and enjoy them but there's a difference between complex and convoluted trash, MGS4 was convoluted trash.
The gameplay left a lot to be desired, there were too many cut scenes not enough gameplay, there weren't many memorable moments. It was very disappointing after MGS3 turned out so well.
Dragon Age 2 -- I think everyone has discussed this games flaws to death in the last few weeks. I knew it was going to be bad the moment its features were starting to get unveiled, Dragon Age 2 was trying to become a Mass Effect clone instead of continuing Dragon Age Origins legacy. The biggest blow was this was the first Bioware game with a poor story.
Others were Metroid Other M, Killzone 2, Mirror's Edge
