Just to let you know, it is illegal to give out games before the due date. On other hands, you're fine, and treyarch probably doesn't care. Oh and your stats may get reset.
Ok, I have a question, is it fun

? What about zombie mode?
I checked into this before, and it isn't illegal, its just stores will be fined up the butt if treyarch knew if stores were handing out games early. For the most part, they probably don't care, since they are using this time to finalize things with their servers, and the people who have copies (however they acquired them) are basically being guinea pigs for the servers (ie small changes here and there). Also, I am very sure they are going to reset the servers Monday, not sure when, don't care, since I haven't played online yet (but i have played around with system link).
To answer you next questions, yes it is very fun! All of the little things they added to the campaign, multiplayer, and of course zombies. The zombie maps are just awesome! The weapons, the traps, the zombies! I can't even find where to begin on how awesome zombies is now. The maps are bigger, several different types of zombies, the creativity of the maps, so cool! As I read what I just typed, I realized I was starting to talk in a circle, but who cares! I can't want to turn my xbox on tomorrow night and start shooting!
Edit: I forgot about the weapons from multiplayer! Flamethrowers! Crossbows! Akimbo shotguns! (no 1887s lol) And if you're from the CS:S division, the galil! The way its supposed to be! Balanced smgs! (No OP umps) Awesome perks and equipment! Sniper rifles! (No quickscoping guys, sorry).
Anything you want to hear about in detail, I'll be on the website most of the day tomorrow, waiting to play online, so Ask your questions!
Edit 2: I knew I forgot something, Double Rainbow!