OK, so first off, who doesn't like to shoot mutant-bugs in a Duke Nukem-esque way? This game absolutely satisfies my cravings to gut some mutant-zombie-bugs...? (I don't know what they're called!)
So you start off in the first level, after you have gone to the shop, and chosen your difficulty and you're dropped into nowhere! Not knowing what to do, but the thing about this game is that you go where you think is right, so if you think it's right to go through that door, or activate that button, chances are, it's the right descision to make.
The game throws you at various types of mutant bugs, shall we say? Of different difficulty to kill, there are some small minor mutants which take a couple of shots to kill, then there are the ones which take an entire clip to kill, and of course there are the bosses.
Now the bosses are hard(ish) to kill because of the fact that you have all the harder mutants to kill along-side the boss, which means that you have to think carefully about how you place yourself on the battle stage with the boss and the other mutants.
There are some moments of the game where the atmosphere of the game is generally decrepit, derelyct, and desolate. But just as soon as you are about to give up... BOOM! Out comes a massive horde of mutants for you to deal with.
Overall this game is really fun, for what it is, and having cleared the first area out in single player, I have no reason to believe it would be worse with your friends. This game is definitely worth checking out.