1. Assassin's Creed II
I've been playing this since getting it from Games with Gold. I was going to take a pass on this entire series since it seemed daunting to catch up on the canon, but this is an incredible game in its own right.
I thought I was done with open world games, but this is an open world you just want to be in. Most of the things you do in this game are fun at a mechanical level.
2. The Walking Dead: Season Two
I played through Episode 1 in a single sitting. While the luster of a brand new game franchise and paradigm is gone, they are still hitting all the right marks with their stories and have improved their UI in how you interact with the game.
I am surprised how dark they get. I don't think a television show would put a kid through what they are doing in such explicit graphic detail.
3. Borderlands 2
I keep coming back to this. (Golden Keys are a nice enticement - good move Gearbox.)