Maybe not the most unfun game I have ever played (I've played games since the late 90s), but certainly the most unfun I have played in recent years: Elex.
I liked Piranha Bytes' old Gothic series a lot despite its weaknesses and idiosyncrasies. The Risen games weren't that great, but the reviews for Elex were pretty promising. So I gave it a shot, and tried for about 16 hours to find the fun in it. I stopped playing when I realised:
- I couldn't hold my own in almost any battle because I didn't have good enough gear
- In order to get better gear, I had to join one of the game's factions
- In order to join one of the factions, I had to perform a number of tasks for them
- The factions were all just dickheads, and I didn't want to do anything for them, much less their dirty work
So yeah, no fun to be had with this one.