I'm going to cheat and pick three, because I have room in my heart for all of them:
Mass Effect 3:
I will complete this post without mentioning everyone's "favorite" part, so let me just say that the other 99% is sheer greatness. The gameplay was improved, the characters were as good as ever, and seeing the ends to all of these plot arcs that I had begun and seen through was something that blew me away and provided some of the most emotional moments I've ever seen in a video game.
Mordin, good sir, I won't forget you...
Journey:
Despite its short length, Journey is worth every penny of the money that I spent for it. It is quite possibly the most gorgeous thing I have ever played, with a beautiful art style and amazing, sweeping vistas. The true source of its greatness, however, lies in playing through with another human being. I was lucky enough to find one partner who stuck with me from beginning to end, and the whole experience was something truly magical. When the end came, I felt genuinely moved.
Xenoblade Chronicles:
I live in America, so it counts. Now that I've played it, I am just eternally grateful that this gem made it to our shores eventually. I still consider The World Ends With You to be the greatest JRPG of this generation, but Xenoblade Chronicles has firmly entrenched itself in second place. Combining the best of the glory days of JRPGs with new and innovative concepts that help make the experience more user-friendly works marvelously, the world is MASSIVE and has enough content for more than 100 hours of gameplay, and once the story really gets going, it keeps you absolutely hooked. It is certainly a masterpiece in my eyes.