Currently I'm in the 20's (I ain't been playing much, just short bursts in multiplayer) and I've been enjoying the assault class (though with the M14 with an ACOG scope). The FAMAS with an ACOG is good, too.
At the moment I've been trying to pass the single player campaign, as I've been digging the story. I just got past the Whiskey Hotel (just after the nuke launch).
I've also been meaning to ask someone: Is MacTavish actually 'Soap' from the original? I've kind of realized this, but having it confirmed would be nice.
Also, the game looks so damn good, graphically, even on a 360 that's astounding - I couldn't believe how good it looked. It must look amazing on HD televisions (I haven't joined that crowd yet, sadly).
On a related note, I would have to say that I love the British SAS missions more so than the American ones. I really enjoy playing as Roach, and if they made a SWAT/SAS/Black Ops game along the lines of COD4: MW2 (same game play, same graphics, same everything - with some upgrades as needed) I would absolutely love it.
I really dig that whole 'mentorship' think they have going, and the group-based aspect (multiple breaching, etc). And I know Rainbow Six does the same, but I enjoy being able to focus on my enemies, and KNOW my AI counter parts don't require me to guide them the whole time - not to mention I think a game concept like above would work well with a 'start as a recruit, and eventually become the squad leader' type of storyline.
In a word, COD4: MW2 is: Awesome.