From everything I've heard that goes for System Shock 2 as well (same developers as Deus Ex), but I can't speak from experience on that one.
Deus Ex was made by ION Storm, and SS2 was Irrational Games/Looking Glass Studios. Warren Spector (DX designer) was involved with the original System Shock though.
And yeah, SS2 is sick sick sick plz plz plz buy it. And DX too. And Freelancer. And Morrowind. Those are prob my top 4 choices from the games mentioned in this thread.