I'm starting with the obvious choice. It's difficult for anything else to compete with this for me. And not just because I have a Geralt-crush, although maybe that too.
I'll admit I was worried about how The Witcher 3 was going to turn out. I loved the first two Witcher games, but was sceptical about expanding it to such a huge open world. Big-budget games are full of the constant need to be bigger and better, and cram more stuff into each iteration of a series. Coolness tends to trump things like remaining coherent and supporting interesting themes.