This is considered my favorite game of all time, and to make sure I have your attention now I'll tell you why :
-Chaos theory has the best multiplayer of any splinter cell
-There are co-op missions that me and my cousin spent countless hours on
-The gameplay is amazing as there is never one way to get through a scenario
-The graphics are still relevant to today's high tech world
Now the detailed explanation.
The storyline is epic. Why is it epic? Splinter cell series has always been known to have a crazy or sort of conspiracy storyline, chaos theory delivers a lot more than that. Two lead programmers that cracked Philippe Masse's kernals from the first splinter cell have enhanced his algorithms and now could be used for any electronic warfare, be it military or economic. One of these programmers is discovered dead early in the game, and the other one on the loose... the story just begins to exponentially get better from there.
The multiplayer was my favorite in this game as it gave me everything I wanted. I want to play online ... okay go ahead. I want to play with my friend on the same screen or at my house and he at his... fine go ahead. Want to play competitively as a spy? Fine. Want to play as a guard and take down spies with a first person view.... heck the devs cared so much they did this too. When someone really gives an effort to really allow any sort of play when it comes to multiplayer, it's greatly appreciated.
I would say the game play of this game is arguably the best type out there. The physics/engine in this one is what would one expect from a third game of the series. I would argue that still to this day even though there are other Splinter Cell's out there, this one still has the best game engine. The soft body touches, the noise system, throwing of objects to make noise, ability to whistle, use the SC-20K it's sniping/assault attachment or it's launcher attachments, the grenade types (frag, flash, smoke), the three different goggle settings (heat, night vision, ECM), ability to either knock out or kill an opponent... there's quite a bit of things to mention. I like the fact you are given a choice of going through vents or alternate ways to avoid conflict or can go through conflict, or one by one slowly "put to sleep and hide the bodies" conflict. The greatest improvement though compared to the first splinter cell is that there is flexibility in the proximity system. When one is close to the enemy, they don't ultimately see/feel you just because they walked past you going through a doorway. This game is fantastic in how you are able to knock someone out or kill someone before they can react. This was a major breakthrough in the series.
How are the graphics still good for an original x-box game? Well how's 1980X 1080 sound? Probably the best we can get unless someone goes through the entire game and re-does it... but there wouldn't be much to redo. The cut scenes are still awesome, and the game play graphics are just as good as any game. You will not have an issue with graphics playing this.
I would highly recommend this game, on sale or not as it is still to this day my favorite game. I'm not being biased in my rating as it being my favorite game, but this game is what took the gaming industry to another level. Thief, Assassins Creed or any of that wouldn't have been without Splinter Cell.
PS - Because I didn't know where to fit this - relevant characters from cutscenes also breif you before going on a misison on top of team members of the echelon.