Good on Ubisoft for taking a chance and making a shooter which isn't in the vein of Call of Duty or Battlefield!
For any of the more grizzled, cranky, older gamers out there, Siege may be for you! No regenerating health, single round head-shot kills, no aim-assist and basically everything I've been groaning about in games for quite a while.
Rainbow Six's charm is also its Achilles depending on what you seek in a game; when you die, you're out of the round; because of that brutality it does tend to set the bar a bit higher, deter certain undesirable types and games and provide a more pleasant group of players (not always, but generally).
I would rate this game higher but there are a few issues. Firstly, some days it seems like you spend a lot more time trying to get into a game than you do by actually playing it; the game does have a few glitches but to their credit Ubisoft are actually trying to fix them and finally, while it does seems to be getting more stable I have never witnessed a console game crash as frequently as Siege does.
All up, while it lacks a little polish, overall as a whole this is a tense, exhilarating shooter for those of us who like a slower, more methodical and thinky kind of shooter. I really dig it.