I'm loving this game, it came at a perfect time with the Halo cheating at a peak and new maps still a few weeks away. This would be my first Splinter Cell experience. I haven't even tried single player yet, but I've sunk a ton of time into the Xbox Live modes.
Vs.- It may be because everyone I'm playing with is just as bad (I'm talkin to you Kyle and Fazer) as I am at the game, but it seems that most of the levels are biased to the mercs. Thats not to say that it isn't fun, I've spent more time in this mode than any other. I'm sure there are technical reasons for this, but I do wish that more than four people could do this.
Coop- Finally a game that took this mode seriously and didn't just rehash single player. It's short, but sweet. With the varied paths to victory, this one will have quite a bit more replay value than you may think.
My biggest problem with the game is the somewhat odd menu system. Compared to Halo, it is crazy to even get to your friends list, and even crazier what to do from there. Squads? I can't figure them out. I wish everyone would just give in and ape Bungie's live interface. Another gripe, though small, is that the three different gametypes don't seem to have any synergy. Choosing Versus mode, for example, takes you to another loading screen and completely different menu style, as well as signs you out of live. Host of a party and want to leave? The entire party is disbanded. Got an invite? You probably missed that message.
I wish I was a lot better at the game, but the fact that I haven't given up says a lot about the game's appeal. I'll be playing this right up until Bungie makes a move, maybe even after. Add me to your friends list if you want to play, i'm on mostly late at night.