I missed System Shock 1 and 2 on release (I was 1 and 6 years old, respectively) but I've recently been playing the SS1 remake and, holy shit, this is an incredible game.
I think the original is held back by its UI but the actual game itself, which the remake pretty much preserves almost one to one, is incredibly solid even by modern standards. I've been super hooked on it and it's opened my eyes to an entire lineage of games that I've not paid attention to - System Shock 2, Deus Ex, and Prey are the big three that I have my eye on when I finish with SS1 Remake.