As you're probably aware, Call of Duty's main attraction is the endless hours of multiplayer and as they bring one out every year, they've plenty of chances to tweak and change it.
However, the phrase "if it ain't broke, don't fix it" springs to mind and thankfully, it seems that Treyarch thought the same too.
The feel of the multiplayer is as you'd expect, fast paced gameplay in the usual categories you'd expect - team deathmatch, kill confirmed, domination etc.
The one major change to the Call of Duty multiplayer is the create a class system. It borrows features from the previous instalments which allow you to unlock guns horizontally rather than vertically using tokens.
The new system is deemed "pick 10" and no longer focuses on choosing one item per slot, instead, you can choose 10 items for your entire loadout.
This means that you don't need to carry a secondary weapon if you don't want to, you can decide to carry an extra attachment for your primary weapon instead.
I have conflicting opinions on this system. It's good because it means that people's classes are vastly different, but it means that people are most likely going to miss out on a ton of content, especially if they don't take a secondary weapon.
As for the game's overall balance, I think it's better than the previous versions of the game - the maps are better than the likes of Call of Duty: Modern Warfare 2 and 3, but perhaps not as well designed as those in Call of Duty 4: Modern Warfare.
One of my main issues with most Call of Duty games is that guns are either massively overpowered or severely underpowered to the point of uselessness. Black Ops 2 seems to have found some sort of middle ground.
There's definitely weapons that seem to be better than others (I've noticed the FAL and pretty much any SMG) and there are also guns that are useless (most assault rifles), but for the most part, each has their own strengths and weaknesses which is what most Call of Duty games lack.