Campaign: Same as it ever was, same as it ever was, same as it ever was, same as it ever was, but vaguely in the future 3/10
Zombies: love zombies, very fun. only downfall is being matched with terrible players, but not too bad. 8/10
Much harder than MW3, same problems as modern warfare.
Maps: Smaller maps mean you die within 5 seconds of re-spawning, or maps are too big that you spend ages running to where you need to go just to get shot by someone camping.
Killstreaks: no problem here i don't think, except a lot of pointless advice you get such as "enemy lightning strike inbound" and within a second of hearing that you get hit and are killed.
Weapons: Some weapons are stupidly overpowered and can kill you in 3 shots which render other weapons useless, some weapons are just absolutely useless and no one uses them, shotguns are really overpowered but can't even shoot someone ten feet away, knifing is a lot harder, be prepared to miss a lot of knife lunges. however, weapons customization is quite useful
Lag and respawn: im happy to say that absolutely nothing has been done to fix these problems, i have very good internet connection, very rarely had the same problems in mw3, i played today and had to quite because every game i was being put in was lagging like hell, don't know why this is such a problem for COD to fix.