If first time being able to play a port of an old game counts...
Tales of the Abyss 3DS
I heard such good things about this game, the combat was fine and functional, and to start off with things seemed like they could get interesting, but it kept having more and more filler, all of it needless, and even the game commented on it. I found that to be one of the strangest choices ever, as the game became more marred by filler quests I found myself bored and distracted, put the game down and had to come back months later, finally finished it and much like my boredom it felt like the writers got bored halfway through when they built up characters and a story that could be something, and then betrayed the player on so many levels and just half assed the ending. The next morning I just wanted it out of my collection.
If only new games count...
New Super Mario Bros 2
Disclaimer: Disappointment =/= bad, though usually do go hand in hand but not in this case. So no it's not a bad game at all, it's pretty great in fact for a platformer, but that's not the record the plumber holds it's being top dog... and this game felt like some homebrew Mario project. After coming off the highs that were New Super Mario Bros Wii and Donkey Kong Country Returns, I'm slapped in the face with a game as simple and basic as the first New Super Mario Bros game on DS, it was like a cold quick shower, then it was over and I traded it in towards New Super Mario Bros U. Which that game is like night and day compared to NSMB2, and so that by far is my biggest disappointment this year, everything else people are mentioning... I either had low expectations to begin with, or don't really care one way or the other, though I recognize these disappointments for various reasons.