If you want to keep it alive, then we've got to get away from calling Marilyn Manson heavy metal!
Go back to the original stuff and move up the eras to see how it has evolved. Believe it or not, the heavy metal era began with Led Zeppelin and Black Sabbath. But it moved into some really great directions with Sepultura, Pantera, and more recently Killswitch Engage. Starting about ten years ago, there was a big ladies in metal movement that I think sort of began with In This Moment, which is a great band that keeps pumping out amazing tracks.
Metal is alive, but like all music movements nowadays, unless it's blonde girl pop it's generally allocated to internet trends.