no, people don't fight because they ''go mad'', they fight because they don't have the same opinion about something. they fight to defend what they think is right.
on topic: this game is a lot easier for people who spend money but you can still enjoy it.
found a bug! when you pause and unpause at the end of a level a new jetpack will fall down on top of the old one, and in boss levels the same boss will respawn with the old old still on screen...needless to say the bosses are the ones doing the heavy pawnage in this game.
with the fail teammates and the human team using "adrenaline boost", the alien story hardly seems fair...still I love the music and the gameplay is very enjoyable.
I really enjoyed this game it's bit short but I guess you can't make this kind of game to long or it would get boring...anyway, the games got good music and lots of zombies to run over.
all in all, it's the most fun I've ever had ''gettin' to da choppa''. 5 stars. :P