According to ESRB, this game contains: Violence, Animated Blood and Mild Language
Parents don't have a lot to worry about, unless they object to the use of guns, rocket launchers, and other various firearms in the course of normal gameplay. The violence mentioned on the back of the box consists of blowing away insane numbers of giant ants, giant bugs, giant robots, giant dinosaurs, and basically anything that qualifies as being a "giant" of any kind. It's all extremely cartoonish and silly-looking, at least in the sense that it's next to impossible to take seriously. The mild language is hardly worth mentioning; I didn't come across anything that was saltier then the language you'd see on any number of afternoon TV programs. There is no sexual content.
Action Gamers—don't be suckered into buying this piece of garbage. A surprising number of reviewers are giving this game a "pass" and calling it arcade-style action. If you ask me, it's a structure-free, crude and artless game that looks like it was created by two guys and a 12-pack. Just because you shoot a gun like crazy and blow away everything that moves doesn't qualify it as "arcade-style"... it just qualifies it as extremely basic and repetitive. If you absolutely must try the game, wait until it's $10.
Deaf and Hard of Hearing gamers won't have any problems. All you need to know is that anything that moves must be killed, and any dialogue even peripherally relevant to the mission is provided through text before starting play. The battle cries and gung-ho shouts of your fellow EDF soldiers aren't subtitled during play, but they have no impact on gameplay and losing them won't affect the play experience.