I haven't played every 2015 I wanted to (MGS 5, for example) but the one that was a surprise was Dying Light. I'm not a fan of zombies in general and I usually don't play survival horror games yet the game mechanics - weapons handling, item managment and especially parkour - was so well-implemented that I found myself devoting around 64-65 hours on this monster. The look of the city was also gorgeous and the various zombies provided different levels of challenge. And they could also be scary as hell: outrunning or manuvering virals at night made for some intense, scary gaming moments. I made a few friends in co-op mode and co-op was so much fun. The most fun in co-op aside from Rocket League.