According to ESRB, this game contains: Fantasy Violence
Parents don't have anything to fear. The main character is a spaceship, and the only violence is watching giant water bugs and space beetles blow up. No blood, no gore, no questionable language, and no sexual content whatsoever. This game is about as clean as they come.
Shmup fans will definitely want to buy this game. Not only is it the only shooter on the DS, it's one of the only shooters on shelves these days, period. Despite the poor choice in implementing the weapon switching system, it's a very respectable game.
Personally, I think it's a better value at $20 instead of $30, but your mileage may vary.
Deaf and Hard of Hearing gamers have absolutely no barriers whatsoever. There is no dialogue in the game, and there are no auditory cues. All vital information is displayed on screen, and I didn't run into any difficulty with the sound completely turned off. Buy it with confidence.