I want to give this game 5 stars...
I loved the 1st Army of Two. I really enjoyed this game too. They improved a few things, but... I had two major issues with this game. The controls of the 1st game were not that fluid. The same is true with this game. I still think the controls for this game could use a lot of work. There are TONS of 3rd person shooters out there with amazing fluid controls (namely games like Gears).
My other problem, which probably doesn't apply to most gamers, was lag. This is one of a very few games that we experience lag. We tried multiple different times, months apart and no change. This game was meant to be played with a co-op friend. That is where it really shines. Just the smallest amount of lag, makes (made) the already lacking controls totally miserable and 100% unplayable.
We play games all the time with no problems at all. This game always had consistent lag. so this problem may or may not effect you. I am playing with someone on the other side of the world, so even with a fiber optic connection, my ping can drop pretty low.
If you can get the on-line co-op to work you will probably play through this game 3 or 4 times. I would have.