Just a few thoughts on other influences / similarities to other SF works...
Starship Troopers - For me, the most obvious parallel is the concept of a coed fighting force. Also, the sheer amount of firepower that the soldiers have to unleash to take down a single alien is another aspect that...
I had a fun time watching this film yesterday evening. While there are criticisms that can be leveled at the film, such as those already posted; for me the tone of the film sort of inoculated the film from most of those concerns. Basically, I "went with it" and had a very enjoyable viewing...