According to the ESRB, this game contains: Fantasy Violence, Mild Language
Parents don't really have a lot to worry about. It's true that the game revolves around guns and shooting things, but the graphics are presented in a very harmless and semi-cartoony style, and there is never any blood or gore. The game's hero runs around and blasts giant bugs and all manner of robots, everything exploding unrealistically. If guns are the issue, then you might want to keep your kids away. But, if realistic violence or heavy levels of gore are more your concern, then this game should be fine. There are no examples of questionable language and no sexual content.
Platform and character action fans will most likely be disappointed in this game. With all of the focus on shooting and most of the other elements taken out, it doesn't feel nearly as interesting or well-rounded as the other three games in the series do. Pick it up used if you must, but be prepared for a very short, very focused experience.
Deaf and Hard of Hearing gamers get a lopsided effort. Subtitles are available during the cutscenes, but there are no subtitles for voiceovers in each level that give background and explain each mission objective in detail. Some levels can be a little hard to figure out without this auditory information, but a little trial and error go a long way. I would not say that this is a significant barrier to gameplay, but it's very disappointing to see such a halfhearted effort, especially from one of the premier PlayStation franchises.