Admittedly, I never got super far in Thief II (still my intent to play it after beating the first one, so... eventually), but I think that second level at the warehouse district perfectly exemplifies what makes those games great, which is to say a big open area with a bunch of guards and stuff to steal, as opposed to the lengthy corridor crawls where there are a bunch of zombies or something. Ugh. That reminds me why I haven't finished the first game.
System Shock 2 was similarly cool from what I played of it, but once again I got stuck. Kudos to you man, you seem to be able to play a game and stick with it for the most part, something I've been attempting to do as of late. It's going... alright.