According to the ESRB, this game contains: Comic Mischief
Parents have absolutely nothing to fear here. Paper Mario is completely appropriate and accessible to gamers of every age and has no material that could be considered objectionable. The only caution I have would be that as in most RPGs, reading has a semi-significant role in the game. Children who are too young to read effectively may have a bit of trouble. Otherwise, this is the type of game that helped build Nintendo's fortune and defined them as purveyors of quality.
Gamers in general can't lose with Paper Mario. Great, cartoony graphics combined with gameplay and mechanics more solid than the Rock of Gibraltar will make this a surefire winner with nearly every gamer. Gamers can expect a playtime that can be as short as 30 hours or as long as 50 hours—depending how many of the subquests are completed and badges found.
RPG fans who own an Nintendo 64 FINALLY get something worth talking about in the genre which was most neglected through the entire span of the Nintendo 64's lifetime. The best part is that Paper Mario isn't only the best RPG on the Nintendo's machine, its one of the best RPGs out there overall.
Mario fans will find a game that treats the world-famous character with the same level of respect and play finesse that Miyamoto himself is renowned for. With cameos from nearly every character from the Mario universe and the same level of charm and style as you'd expect from a first-party offering, Paper Mario hits the mark on every level and provides a phenomenal addition to a legendary series of titles.
Deaf and Hard of Hearing gamers will have no problems here since all of the games dialogue is presented through text, and there are no significant auditory cues.