Looking for a FPS with a good single player campaign. Suggestions?

[pots555]

Wow!  Thanks for the replies.  Well, I got a good deal for Metro 2033, so I decided to go with that.
So far, I am very impressed by the atmosphere. 

I guess The Orange Box and Bioshock also sound pretty good.

Unfortunatly, I only have an xbox 360, so I won't be able to try Killzone 3, and from what I have seen, it looks really, really good.

How about Battlefield: Bad Company?  I just saw it pretty cheap at Gamestop.  Just wondering.

Thanks!