Mine was also The Witcher 3: Wild Hunt. Awesome gameplay, epic story and probably one of the best looking games ever (on PC of course).
Some honourable mentions for me:
Metal Gear Solid V: The Phamtom Pain
Batman: Arkham Knight
P.S The Witcher 2 is pretty good but not as open world as The Witcher 3..and the first Witcher is pretty bad...