I don't think there's any particular game that really stands out as truly disappointing to me, but I think I was prepared for the worst. This year has been pretty lackluster as far as franchise titles and hype, but I do admit some of the lesser known titles really surprised me.
I could see the writing on the wall with Dead Space 3 as more videos came out, but I was willing to give it a shot. It was a decent action game, but the core concept of the series - horror - was lost. The F.E.A.R. series did the same thing, sadly. Thankfully a lot of the indie developers pushed out some nice stuff this year in the genre.
Amnesia: A Machine for Pigs - turned out alright, but compared to the original it was weaker.
God of War: Ascension - obvious cash grab, boring and repetitive.
Legend of Zelda: A Link Between Worlds - Its a good game and I'm enjoying it, but the fact that its a pretty heavy Link to the Past clone really still grates on my nerves. The biggest reason is the price tag: 40 bucks? Nintendo practically copied and pasted 60% of LttP to this game, it should be $20. I'm glad I got the Zelda DS during Black Friday, so it wasn't like I got robbed, but I feel bad for other people who paid full price. They should have at least gave a copy of LttP to download for the 3DS as part of the purchase.
BioShock Infinite - I'll agree with some of the other input, it wasn't as big as the hype. Good game? Yeah. Game of the Decade? Definitely not. The story was fine, but the game play was pretty dull. The voice-acting made the majority of the game, though. The tie-in at the end was strong. However, the overall game needs to be awesome. That's like saying you love X movie because of the one part at the end. I loved the part of Return of the Jedi where Vader tosses the Emperor down the shaft at the end, but I'd be a heathen to claim it was a better movie than Empire Strikes Back.
I hope Dark Souls 2 never makes it on to next year's list.