1. Resident Evil 6: It wasn't the worst game ever or anything, but I was totally let down. I even loved RE 5, but this game missed the mark somehow. I liked the changes in some of the mechanics, but the inventory system was pretty awful. I think the game tried to recycle too many things from RE 5, and the plot got a little too ridiculous to be funny anymore. It was just an okay game, but I wanted to be great.
2. Silent Hill: Homecoming: This game got an "action make-over" like many other console horror games, and it really, really didn't work for Silent Hill like it did for RE 5 and Dead Space 1. The sense of tension is greatly decreased when your character has brutally effective finishing moves and great aim with a firearm. It seemed like very little of the grotesque imagery had anything to do with the story, which is one of the franchise's strengths when it decides to use it. It was very disappointing since I loved all of the previous Silent Hill games. It's been a fairly bleak generation for the franchise.
3. Perfect Dark: Zero: It almost made me regret getting a 360 so early.
4. Vikings: It seemed like a really cool concept, but the game play was very repetitive, and it felt generic/uninspired. I didn't even finish it.
5. Tales of Symphonia: Dawn of the New World: I loved Tales for the gamecube. It was a fantastic RPG, and one of the only multiplayer ones that I've played. The story was a bit slow, yet interesting with a few twists, and the game play was excellent. The sequel couldn't seem to get off the ground at all in terms of story. There was so much densely-packed dialogue, even after the first few hours, that it seriously hampered the pacing. This is especially unfortunate since the characters, story, and writing seemed far inferior in the sequel. My friend and I couldn't stick with it since the battles (the only good parts) were so few and far-between.
These are the ones that got me. They weren't necessarily the worst releases, but they were the most disappointing.