My actual biggest disappointment would be related to gamers themselves this year but let's not open up that can of worms.
In terms of actual games, hmmm.... probably Watch______Dogs. I was totally stoked for it. I tried to not get too hyped up, but I just loved the concept behind the game with all the hacking and fancy business. I thought that would be way cooler than it was. The city itself was boring as shit too. Not as futuristic as I had hoped. Where is my neo-punk deck-diving open world game people? God damn it will someone just make one already?