According to ESRB, this game contains: Mature Sexual Themes, Mild Animated Violence
Parents should be aware that .hack isn't the most accessible title for the kids. While it isn't offensive or gratuitously violent, it's definitely aimed at a more reflective teenage-and-up crowd. And if the kids do happen to like it, you'll be shelling out for the other three volumes in the series as well.
Fans of anime should eat this title up. There's an option to set voice-overs to Japanese for a "more authentic" experience, and the development team includes anime creators Yoshiyuki Sadamoto (Evangelion) and Kazunori Ito (Ghost In The Shell). There's also the full-blown anime series, .hack//SIGN. Fans of role-playing games should appreciate the innovative concept and strong storyline but may have reservations about the battle system.
Casual gamers will likely not be interested in investing the time and cash required to see the series through and will find INFECTION unfulfilling as a stand-alone title.
Deaf and Hard of Hearing gamers can turn on subtitles for the movie dialogues, and have text bubbles for the rest of the player interactions. There are sound and music cues to indicate approaching monsters, but these are accompanied by obvious visual cues as well.