According to Steam, I spent most hours this year playing Book of Hours. (The word "Hours" is in the name of the game, so what choice did I have?) It is an amazing game, and I recommend it to anyone who likes cozy games with lots of lore to explore.

However, there is one game that I must confess I had even more fun with, even though it's relatively short: The Pristine Cut of Slay the Princess.
I can't really say much about it other than that it's a horror visual novel with excellent voice acting and incredibly good writing, as almost any detail of the game's story would be a spoiler.

(Edit: I know, both of those games released last year, but the question was about which Steam Replay and which games one had fun with this year - not about games that released this year.)