Many ... the ones that come to mind for this gen though ...

-Brink : I can actually remember talking my friends into buying this laggy Team Fortress 2 ripoff at full retail price. Ugh, I was so embarrased and saddened by how awful and downright unplayable this game was.

-Dead Island: I think everyone was expecting a very very different game from that first intriguing trailer. We ended up with a watered down sandbox style Left 4 Dead.

-Silent Hill Homecoming: I had some hope for the series even after Origins (I figured it was a PSP fluke of a game). I was still in denial about the future of the series, and I honestly thought there was a chance for it post Team Silent. Boy was I wrong. This series (much like Resident Evil, F.E.A.R., Dead Space, Alone in the Dark, and anything resembling a survival horror franchise) had the soul ripped right out from it which left us with a product that is Silent Hill in name only. The genre is dead, and I don't think The Evil Within will change that (probably will pull a Dead Island and be a completely different game when it is shipped as compared to the original concept).

Dishonored: This was by no means a bad stealth game, but it can't hold a candle to the amazing Deus Ex HR we were treated with just a year prior in 2011. The stealth mechanics were clumsy, the story was MIA, and the setting/art design was beyond ugly. 

top 3 most disappointed game(s): L.A. Noire. Final Fantasy XIV. Rage.

Never!

**cough**

FAR CRY 3. Major step backwards.
SIM CITY. Now Sim Village and online MMO.

Yeah, yeah, I know, it's the best game ever or whatever. I shouldn't have to complete a game before I can enjoy playing it. I understand the time mechanic fine, I knew what to expect with that going in. The game just doesn't hold my interest. I made it pretty far, too -- got three boss masks. I really like the dungeon design, I think it's some of the best in the series. The third boss may have been the worst boss battle in the series. Just terribly designed.

And the smattering of sidequests does not make up for the general scarcity of content.

But -- if I finish the game, then play through it a second time, and at some point get every mask -- then am I allowed to dislike it?

L.A. Noire - as others have said, huge hype, great concept, terrible letdown.

Dragon Age - I got a PS3 in 2010 (only had Wii before) and heard that this was one of the great games of the generation. Turns out it was a tedious and thoroughly bland mess of a game.