ames Bond is a wuss. Ditto that Mission: Impossible dude. Even 24's Jack Bauer is a little gun shy compared to Sam Fisher, the National Security Agency's most-elite black-ops agent. Well, Sam is back in Tom Clancy's Splinter Cell Chaos Theory, a mouthful of a title that offers a lot of bang for the buck. The mission? Stop Japan, China and North and South Korea from starting World War III. Nothing complicated.   But Sam isn't flying solo this time, and neither are you. In addition to 11 Sam-tastic single-player levels there are four co-op missions requiring you and a buddy to take control of two younger Splinter Cell agents. There's the usual arsenal of smack-talking, neck-breaking moves from single-player mode (where else can you taunt an enemy while you slit their throat?) along with 10 or so co-op moves that make full use of the buddy system, including simultaneous double assassinations. Be warned: No matter how bad-ass you are, you can't beat any of the missions alone; if one of you dies, the mission ends.   Adversarial Mode is back in force as two mercenaries face off against two spies in any of 11 large maps and with enough Q-inspired gadgets and weapons to make a snake eater jealous (thermoptic camouflage suits, something called a "sticky shocker"). Story Mode offers multiple objectives, Disk Hunt sends players racing to collect exactly that, and Deathmatch is just what it sounds like-spies versus mercs, no holds barred. Just watch out for the new merc Berserk Mode moves.   The only downside is that not every system is getting equal treatment: No adversarial mode for GameCube (although there is a split-screen co-op), and PS2 has co-op (but not online) and an adversarial mode that lacks the new additions seen on Xbox and PC. For the complete package, that means Xbox and PC.                                                                (Ubisoft; For Xbox, PS2, GameCube, PC)