This game is great by itself but it's best when played split screen!
The 300 weapons in the game are just too cool to begin to describe. I've seen a gun in the trailers (pesticide gun) that allows you to fire a nuke that can obliterate a city block.
The only gripe I have with this game is that the mini-map icons for you and your partner are not very obvious. Whenever you start a level you have AI companions along with your co-op buddy and sometimes the green squares that represent both your co-op buddy and your AI companions get confusing.
The music just sounds mostly of disaster film orchestral scores and some action film music. There aren't any faults about the background music but it's not going to get anyone humming the tune either.
Another selling point of this game is that it's priced relatively cheap to major titles (many block-buster titles cost $60).
update: I played it some more and I reached rank 5 for the battle armor and the weapons keep getting better. There is a manual-lock-on missile called the air tortoise that drops randomly (usable only at rank 4 of battle class). The air tortoise fires a missile that does crazy damage (9999) but it's flight is so slow that even the battle class can out run it. It looks hilarious but I actually beat the first level of the game on inferno difficulty with this launcher.
I've also played some more with the other classes and I feel that the battle class is overpowered compared to the jet, tactical, and trooper classes. Sure, the battle class runs really slow but the attack animations of the ants are usually too slow to hit as long as you're moving away from them.
The AI for the squad mates has so far proved fairly competent revive-wise. The only time they didn't revive me was when I was swarmed by a whole screen full of ants. One thing to note is that there is friendly fire (that cannot be toggled off) and sometimes the AI squad mates fire a missile into an ant hill expecting to kill an ant on the other side but hits me and interrupts me from blowing up the ant hill with an explosive charge. AI buddies also have a problem staying away from big enemies that do big area damage (robot mantis). It seems that all AI buddies are good for are diverting the enemies attention and reviving you (bomb spiders don't swarm you as hard). Once you start playing with a real person you really start seeing the deficiencies of the AI buddies.
Note on survival mode: I think survival mode is a little bit pointless because you can't bring your elite gear from the campaign to duke it out with waves of bugs, robots, and ships.
Note on endings: There are multiple endings. In order to get subsequent endings after normal you must complete the same levels on hard and inferno mode.