Pros: Rewarding multiplayer (on/off-line), wonderful story, great controls
Cons: Odd glitches, and slightly off enemy AI.
The bottom line: I would say buy. With the new "Throw back pack" of maps for it on XBOX live, it will be the gift that keeps on giving.
Having not been a fan of Rainbow Six in the past, much to my friends dismay, I was not looking forward to this next gen title. Much to my many hours of amusement, I love this game. The story takes place in a future time set with many ties to the other Tom Clancy games that people may not know (and I'm not telling).
I really like how they took to way they did Ghost Recon: Advance Warrior style of play and really worked with the Rainbow Six engine to make a really well oiled playing scheme. The controls feel a lot better than those before it. Being a fan of Ghost Recon, and some of Clancy's other games, I was really amazed with how this game felt.
The enemy AI is amazing. They react as a real terrorist would in those situations. They will head towards sounds, or towards suddenly open doors, but not without certain cautions, or flanking attempts. Although sometimes I had some odd glitches with the game and AI. The game sometimes would freeze the 360, or the AI would just stand there and stare at me until I shot them. It was a bit off every once and a while.
All in all this game was an amazing success and has me hoping to see another Rainbow Six soon, and maybe an End War style to boot.