According to ESRB, this game contains: Violence
Parents don't have anything to worry about. There is no questionable language in the game, and no sexual content. The "violence" mentioned by the ESRB is basic, run-of-the-mill shooting and punching. Although this violence does take place against humans (as well as robots and mutants) it's not at all explicit or gory. Parents with aversions to gunplay may want to steer children clear, but I'd say this content is suitable for most players, as long as they can handle the difficulty level.
Shoot-‘Em-Up and Action Fans will find an absolute gem. Not only is the game a perfect melding of two fading genres, it's a great example of the sort of gameplay that we very seldom see stateside in the current environment. It's safe to say that this game easily earns its "hardcore" stripes and will bring a smile to the face of anyone who can enjoy old-school sensibility.
Deaf and Hard of Hearing gamers will have no problems. There is no dialogue during gameplay, and all conversations between levels are presented through text. Although many characters do give a scream or a moan when they are defeated, it's a very insignificant cue accompanied by a visual signal. I feel comfortable in saying that this game is completely accessible and will present no communication barriers.