According to ESRB, this game contains: Animated Violence, Mild Language
If you're a fan of 3D action and adventure, and you think 2D games are Stone Age, then Bangai-O definitely isn't for you.
However, fans of fast arcade action now have a truly great one for Dreamcast. Bangai-O is a shooter with personality and charm, and that's pretty rare these days. As a 2D game alone, it humbles Capcoms Giga Wing—the only other 2D shooter for Dreamcast that I can think of—without even trying.
Treasure fans should add this one to their collection immediately. If you liked Gunstar Heroes, Guardian Heroes, Radiant Silvergun or Silhouette Mirage, you'll love Bangai-O (one of the levels in the game even pays tribute to Gunstar Heroes).
Parents need not worry too much about their kids playing this game. It's harmless arcade action, though there are tiny screams when you blow up enemy households, and there's some adult innuendo during a few of the conversations.