I have the full game on 360 and PC, my PC usually gets more playtime as I'm in a huge multi-gaming clan (TAW).
Highly recommend the game and only scored it 4 stars because there's no 4.5 - once Ubi fix their master server lists for PC I'll be happy to let it have 5 (which it deserves on 360)
The HAWX missions are pretty fun in single player, but really come to life in co-op mode. The PC co-op mode is having problems connecting at the moment owing to Ubi's master server not updating properly, but the 360 Live version works perfectly.
You level up in the game like in RB6V2 and CoD:WaW, with ranks awarded for XP gains, and XP gains for kills and completing tasks (like shooting down XX enemies with a particular type of missile). Each rank gained unlocks extra planes and weapon packs. This gives even single player missions replayability as you decide to destroy ground targets with cluster bombs this time instead to get the extra XP points, for example.
In co-op mode you can choose any mission and have 3 players join you to complete it, the twist is that for every additional player beyond yourself the game adds more enemies and ramps up the difficulty! Great fun and can get very hectic as you try to co-ordinate who is going to destroy what - hehe.
Flying in HAWX is sheer adrenalin fuelled fun. e.g. You dive out of the sky to nail a tank that is nestled between high rise buildings, peel out and then realise that the same high rise buildings are now blocking your exit route so you quickly flip the plane 90 degrees in the air and shoot through sideways between two of them. Or perhaps, you are engaged in a furious dogfight, outnumbered and trying to protect a bomber flight, or even a presidential plane, wheeling, braking, diving, trying to get that LOCK so you can blow them out of the sky, all the time watching them get nearer to your protected plane and hoping you get them before they get it.
I bought the Saitek AV8R-02 (360/PC) Flight Stick for the game and have not regretted it. Playing the game with a joystick is way more fun than a control pad or keyboard/mouse.