Best series ever..I even loved Deadly Shadows, which evidently alot of people didn't.
I think alot of folks can't take the slow, methodical pace of the first two games.
But yeah, freaking incredibly awesome, and hold up well even by today's standards.
Also it's a game with alot of style, which nobody has these days
If you like thief 1 & 2, you owe it to yourself to check out Darkmod if you haven't already...
Especially if someone can't take the old graphics, Darkmod runs a modified version of Doom 3 engine, and plays almost exactly like Thief 1 and 2, with a few notable additions. It looks quite nice with the right mods...seriously, any thief fan will love it IMO.
The only modern-ish game i'd give a Thief style nod to is Deus Ex HR...nowhere near the amazing experience of the original Deus Ex (but what is), however it's the only other stealth game i've played in years that I could take seriously and get into very much.