I'm surprised nobody here has mentioned this game. The 2017 remake is fantastic! Essentially it is very similar to System Shock 1 and 2, in terms of being free to explore and alone in a world that you must figure out as you go along. Combat, while intense when it happens, is not the focus, with exploration and problem solving being bigger components. Plus it is true hard science fiction, a rarity in PC gaming in a first person perspective with a Shock/Ultima Underworld platform.
If y'all haven't played the game, you should.
I have not beat it yet, but I'm about 15 - 20 hours in and have been having a great time.