OK, I've managed to play through this over the past couple of weeks & have been introducing some friends to it as well.
It's a tough & punishing game - if you run & gun you will not survive...literally! It's like playing on Veteran Mode (Call of duty Series) even on standard difficulty settings. So if you bash down a door & run into a room blasting at everything in sight - the enemy AI will get them hiding & ducking for cover, then proceed to light you up with heavy automatic weapons!
However, the key element is stealth.
I first started playing it with Sparks in co-op mode - a seriously challenging 4 levels which take in everything from infiltration, evasion & straight up rooms full of guards that you have to dispatch quickly & silently. It was a real team match & a proper challenge. In fact it was a welcome break from the intensity of CoD6:MW2!
There are some differences in the controls & there's a good cover system (a la Gears of War) which is very natural feeling. The weapons don't initially look very good, but they each have 3 potential upgrades which add things like extended mags, higher calibre or range bullets & in some cases scopes. There are also some cool gadgets - there's the standard frag & flash grenades, but also a sticky camera (which I've not really used that much yet) a very useful EMP grenade for knocking out the lights. However my personal favourite is the remote mine - it's like the C4 from CoD, but with much more range & immensely satisfying to use - it always make me chuckle!
The stealth elements are similar to another Ubisoft title - Assassin's Creed 2 - so you can climb on multiple surfaces (not all though a la AC2) like pillars pipes & rails, then rain down some 'Death from Above', or if you can sneak up to someone (crouched & from behind naturally) you can take them out swiftly & silently & it's immensely satisfying to do. You can also grab people who are foolish enough to peep out of windows near to where you are hanging from the ledge. If & when you do manage to do something special (not just shooting people in the face) the reward is a one-touch assassination - you hit the Y button & then your character will pop out of cover & do an impressive single shot kill.There are also some interrogations, which seem to have been influenced by Jack Bauer - gritty is all I'd say!
The main story seems to also be influenced by both 24 & CoD6: MW2, which is not detrimental at all. In fact there is a little bit of the Jason Bourne series as well. There's lots of variances on a theme (infiltration, extraction, etc.) but it's a very satisfying game to play & I would class it more in keeping with AC2, rather than the blammo action of CoD.
Another thing worth mentioning is the fact that Ubisoft are doing something unusual in the gaming world - giving you free 'stuff', just for playing the game well - there are achievements of course, but what the publishers have done is to release some DLC with free guns & equipment - every week there's something new to try. It doesn't feel lazy - quite the opposite - it feels like they're giving something extra - to try to keep you playing the game longer & that's definitely no bad thing.
Overall 4/5 only because the controls aren't completely intuitive but a solid 4, for sure!