Hey JB,
You and I have similar gaming tastes, so I think you'll like NOLF. I'm about 2/3 through and it is a lot of fun. It's not semi-non-linear like DX and not as precision stealth oriented as Thief, SS2, or DX, but it is a lot of fun. It DOES take a particular sense of humor though, so if you haven't tried the demo you may want to for that reason alone. If you don't find the humor to your liking, or at least tolerable, then you may find the game silly or annoying (I find it hilarious at times).
It took me about 2 levels to get into it, but now I really enjoy it. It's kind of "DX Lite" since it doesn't have the RPG elements. The AI is EXTREMELY good. Bad guys take cover, use interlocking fields of fire, run away if they get caught alone or hurt, etc. My only complaint is that it's the first game I've had to run at less than 1024x768 at 32 bit color/textures since I upgraded my rig (C533A@825/GTS 64MB 220/400). It runs fine and looks good at 800x600 though. I also found the interface a little inelegant, but not distractingly so
Anyway, if you like the demo and can get the full game for $29.99 or less, buy it.