Arx Fatalis had a bunch of unusual and interesting game systems. Lots of cool environmental interaction (things like cooking food items by placing them next to a fire or your fireball spells lighting up nearby candles and torches). Immersive.
Unfortunately the game had many puzzles I had to look up solutions for. I think the puzzles were generally fine and presented with sufficient hints; I just happen to have a weak brain and short attention span for that sort of thing. More a problem with me than with the game I suppose.
I played it using the Arx Libertatis (https://arx-libertatis.org/) sourceport on Linux and that seemed to work very well. (My only major complaint is with the collision detection; it seemed easy to get stuck in map geometry, particularly some angled walls and steep floor slopes).
Anyway. Game is good & I kinda want to study its maps for Quake mapping purposes.