You can also try Velvet Assassin, it's not that bad IMO.
Yeah, I had read some awful reviews back in the day, and thus avoided it for years. Then I downloaded it from Amazon last year, and really enjoyed it a lot. The stealth is very specific in what you can do, and the game is very linear, but I had a great time with it in spite of all that. Also, the Amazon d/l version I got has zero DRM, not even Amazon's activation wrapper.
However, I have to agree with Wargnthoi up there: No other game has ever come close to replicating the "Thief" experience. And as far as I can tell, no other game has even tried. I've looked far and wide. This lack of imitators baffles me.
Your best bet would be to locate the best fan-made missions, or sets of missions.
And don't forget "T2X: Shadows of the Metal Age" for Thief 2: A fan-made mission pack that very nearly equals the original games in terms of quality. I was seriously impressed. It is excellent.