This is the toughest yet for me! The Witcher 3 and Metal Gear Solid V: The Phantom Pain blew me away, I ended up loving those more than I could have dreamt of. Before playing those I was not really the biggest fan of open world games, but the way those two handles their game worlds really won me over. The Witcher 3 is just packed full of content, life and character. The quests are all so creative, well written and well designed, even the side quests. MGSV is a completely different take on the open world design, where emphasis is on systemic world design, with lots of options for the player to experiment with the mechanics of the game to complete missions. It is almost a coin toss for me, but I have to go with The Witcher 3, as MGSV does have some flaws that take it down just a little bit, such as main missions that repeat with new rules in the last third of the game, they are mandatory to progress the story, but should really just be side content.
Another major honorable mention is Her Story, one of the most unique pieces of interactive storytelling I have experienced.
Ori and the Blind Forest is also an amazing metroidvania, I think I prefer it to the sequel.
