Thief

[Hong Kong Cavalier]

...is now available on Good Old Games. (And it even works on XP/Vista/7 now)

http://www.gog.com/en/gamecard/thief_gold

This game has to be one of my most favorite franchises ever. The graphics are 14 years old now, and the AI isn't the best compared to the current crop of games, but Thief had the best atmosphere I'd ever experienced. If you enjoyed Bioshock (and are looking forward to Bioshock Infinite) you owe it to yourself to drop the $10 on this game and play it.

Many of the elements that Irrational Games used in Bioshock were first developed for Thief (by the same people) and that, more than anything was why I bought Bioshock.

A word of waring: this game takes patience. Lots of patience, as you are a thief. You don't have guns. You're not wearing chain mail armor. You slip in the shadows, you incapacitate guards (and hide them somewhere out of sight), and pilfer goods from under the noses of unsuspecting nobles.

A short discussion with Irrational Games developers about Thief:

[Mayberry Machiavelli]

1. Stealth games in general rule, Thief rules!

[Glassunion]

2. Eidos Montreal is currently working on #4...

It is taking them forever to get the new one out.

[Hong Kong Cavalier]

3. They did Deus Ex: HR. And they're doing DLC for it, too.

Based on how well I enjoyed DE:HR, I think they'll get it right. *crosses fingers*

[semillama]

4. Thief: Deadly Shadows was one of my favorite games for the original Xbox

I still have it in fact. I never played any of the others, though. It's definitely one of the franchises that needs another entry.