Synopsis: After a tragic scene with the murder of his friends, Brandon Heat follows his only friend Harry McDowel into Millennion, the largest mafia syndicate. While Harry McDowel is striving for power, Brandon is only staying in Millennion to see the girl he loves whose custody was gained by the leader of Millennion, Big Daddy. But as the years pass and Brandon proves loyal to Millennion, Brandon learns the true purpose and passion of Millennion, and that's when true conflict arises.

This is one of my favorite anime's ever. I'm currently rewatching it. It's truly an anime anime.
what for Genre has the Anime?
It was a very good anime.

Good plot, good plot progression, good characterization, I vaguely recall a good ending too.

The soundtrack was poor.

It's genre is probably guns/action.
http://myanimelist.net/anime/267/Gungrave

I rated it a 9, impressive.