Starcraft has been my surprise of the year. Played a ton of Brood War and WoL, but I kinda soured on everything after HotS.
But Legacy of the Void is put together so, so well. Even got me to put down Tomb Raider, and I love Tomb Raider. Might even delay the Bloodborne DLC for me.
Big problems I have. 2015 has been an amazing year.