Gonna come out swinging. Have to say BioShock Infinite. Hated the chosen time period, the odd stab at racism, the characters, and the total vibe of the game. For me, the game was a complete MISS..and graphically on the 360 I think it was very drab and uninteresting.
I can't think of too many. Maybe Resident Evil: Revelations. I was hyped for an RE game that everyone said was better than 4 and 5. What I got was a crappy plot and a game that indeed felt like a 3DS port.
Perhaps tied is Aliens: Colonial Marines, just because I was a huge fan of the films and actually thought Gearbox was going to honor them.
Have not been disappointed by anything I have played from this year.
Aliens Colional Marines never had high expectations because it was an Aliens game, it met my low expectations.
Sniper Ghost Warrior 2 was a fun relatively short game, playing the first game now and it is like a whole different experience full of bad game design compared to the sequel which got a whole lot of things right. It is like a Mega Man vs Mega Man 2 or Street Fighter vs Street Fighter 2 series jump in quality.
Castlevania Lords of Shadow: Mirror of Fate was a enjoyable experience for me actually. I was glad for no more IGA crap on the handhelds.
Aliens: Colonial Marines What was shown in pre-release game-footage was NOT even a representation of the final product. Gearbox pulled a fast one with this, and I wish Sega would sue their asses. It looked so good in Preview builds...but what they delivered was something different than promised.