Tom Clancy's Splinter Cell: Chaos Theory is prolly the best stealth games this year.
Of course you have the normal Solo missions, but the new aspect of this 3rd installment of the series, we are introduced to the Co-op missions. Even though there are only 4 (5 counting Training) it's still fun to play, also, you can play it online, which gives Co-op a pretty good appeal.
Theres also a Versus mode, but I really never got into that, you'll have to find another review about that.
The graphics are very, very beutiful. But it's all ruined by how dark most of the game is, and is actually very hard to notice with night vision.
One thing I must complain about is the AI. I don't know why, but sometimes I just feel the gaurds are so stupid, even on expert mode!
Tom Clancy's Splinter Cell: Chaos Theory is packed with alot of stealth action. If you are a fan of the Stealth/Action genres, it's a total buy. If you're new to the genre, try renting it first, and see how it plays out.