I recently booted up Half-Life 2 to replay it. I have played the absolute shit out of this game before, so 60% of it just feels like a drag to me now. It was such an amazing game but it's sort of spoiled for me after I've played it too much.
I also discovered ULTRAKILL a few months ago. I feel like I could play that game forever. It has tons of content, weapon combinations and higher difficulties with different enemy behaviour.
Do any of you have more game suggestions like Ultrakill? A really replayable singleplayer game.
!!BTW I don't mean online multiplayer games or games similar to candy crush!!
War for the Overworld (I have many thousands of hours in this)
Settlers 2 Gold
(Both the above have a lot of user generated maps, which has given them most of their longevity.)
Factorio