|Firstly I'd like to note that I have NOT played the multiplayer or zombies portion of the game yet and cannot comment on those. Got to leave something for someone else to write about!
Black Ops 2 is the first Call Of Duty game in many years that has attempted to do something new with the series while retaining at its core what makes Call Of Duty what it is. Treyarch have managed to make a genuinely interesting story, and while it has a couple of predictable twists and some absolutely laughable voice acting in places it's definitely one of the best CoD stories in the whole series. One major addition really stands out; the ability to choose your own loadout at the start of a mission, choosing your own weapons, attachments, grenades, perks, etc.
Gameplay is your typical CoD fare; 2 guns, 2 grenades (or gadgets) and a lot of running, crouching and reloading. The gameplay is slick and well refined (as you'd expect so far into the series on the same engine) with the guns feeling satisfying to fire and enemies reacting appropriately to getting shot, stabbed, burned or blown up. The game supports both keyboard/mouse and a gamepad out of the box with all the standard remapping and sensitivity options you'd expect. Level design lends itself well to the gameplay with most missions offering multiple routes to an objective and some even changing depending on how well you play (I won't go into detail on this because it's spoiler-riffic but the feature is prominent throughout the whole game).
Sound design is also surprisingly good for a Call Of Duty game, this is perhaps the first where weapons don't sound like pop guns and even the small silenced weapons (for example an MP5 or Makarov) don't sound like a lazy fart in a tin can. This attention to great sounding guns is a welcome addition but it does sadly draw attention to other flaws in the sound design such as certain inconsistent environmental sounds, bad voice acting (at least two characters are consistently terrible throughout, with their performances being absolutely laughable every time they open their poorly lip-synched mouths). Those problems aside however Treyarch have done a great job with the sounds and the different 'mixes' in the options allow for boosted bass, or high and low end sounds, or both. There's even a hearing impaired option that boosts voices in the game (which even though my hearing is fine, I turned on to investigate and it acts like a ducking effect, though far less conspicuous and is surprisingly good).
Graphics are my big gripe here, not because they're bad but because the maximum resolution you can set the game to in the options screen is 1600x1024. My screen is a Samsung HDTV that often crops the edges off of lower end images that don't meet one of its resolutions and so running in full screen makes my device assume 1920x1080 and upscale the 1600x1024 signal so that the picture is cropped on all sides, making most of the sparse in-mission UI completely useless. That said, the graphics options otherwise are just basic CoD stuff, they've pretty much been the same since Call Of Duty 2. Of note however is how Vsync causes framerates to dip by as much as 30-40 frames when aiming down the sights of a weapon. Meanwhile the graphics themselves are outstanding for the IW Engine it's still not a visual marvel ala Crysis. Little details really stand out, like the Millimeter Wave Scanner sight's ping (highlights enemies) still being in effect through the sight even when the weapon is at your hip.
Design; the obvious elephant in the room since most would argue that Call Of Duty games have had no originality in several years. However, Treyarch have definitely stepped up to the challenge and managed to make a Call Of Duty game adapt to your actions and skill with the story taking different (though minor) routes, characters living or dying based on your actions and choices and a good clean UI that gives you what information you need without clogging up the screen. Level design is also less linear before but no matter what route you take you're never going to find yourself at a different destination than where the game wants you. Treyarch have paid great attention to the little details in things and while that's a good thing it does accidentally draw your attention towards the blatantly obvious flaws (for example one mission where your illusion of choice is completely shattered by being forced to take a particular action via an instant fail condition if you don't).
Overall: I personally find this to be the best Call Of Duty yet. It still apes its predecessors very closely in terms of gameplay and attitude but it also adds enough depth to keep it fresh and interesting. It has the best writing yet and features a robust and moderately lengthy campaign that is satisfying right up to the end. The few flaws it has are only made more blatant by the otherwise high quality and some characters are genuinely likable and are portrayed well in their third person models and animations (one scene in particular actually had me feeling bad for one of them). If you're not already a fan of the series then this isn't likely to change your mind, but it is a big step in the right direction and Treyarch have definitely earned their stripes with the campaign.