Torn between 4 for different reasons, so it's a joint 1st place for all 4:
The Witcher 3, because its just a masterpiece of storytelling, quests and beautiful game design all together in 1 fantastic package.
Subnautica, as someone else has posted, it just sticks with you long after you've finished it. Also very atmospheric (and in VR utterly terrifying!)
Ori and the Blind Forest, for gorgeous art style, great gameplay, amazing soundtrack (listening to it now in fact) and those feels at the start
Factorio, because it was the first game in about 10 years that had me playing "for a couple of hours" only to realise its 4am and I have to get up for work in 2 hours...