What impresses me about the game is the teamwork aspect. You find you and your partner pinned down in an urban environment, while in most games you would either try to snipe the opponent or grenade him into submission, Army of Two is no ordinary game. While those remain viable strategies, AO2 encourages more team oriented solutions. In this case, I ripped the door off a nearby car and carried it like a riot shield, while my partner fired over my back. Other situations find you outnumbered and outgunned with no cover in sight, so you go back to back with your partner in an adrenaline filled shootout with the enemy.
Also interesting is the incorporation of aggro into a shooter. Aggro's normally a staple of MMORPG, but the way it has been implemented makes sense. For those who aren't in the know, Aggro is essentially the enemy's attention. If you start shooting, then the enemies focus their fire on you, if your partner is shooting, they focus on him. If you both shoot, they focus on whomever has the biggest gun.
Stylistically, the game looks real good. It's got a real edge to the characters appearance, the masks kind of make them look like Jason goes to War. The Characters have real character, however, the enemies are kind of bland. If they were in Star Trek, they'd be wearing a red shirt and be dead by now. In AO2, they were turbans, and are dead already.
The controls could use some tightening up, but that's really my only major complaint. It's soo much fun in Co-Op mode though.