Metal deserves to be a top-level genre with all of the current Heavy Metal sub-genres nested under it.
Currently, Heavy Metal and all its sub-genres are nested under Pop/Rock. Focusing is an extra annoying click. Metal has about as much to do with Pop/Rock as Reggae at this point. Come to think of it, what does pop have to do with rock?
Admittedly this is all very personal stuff. Perhaps the larger issue is that users can’t rearrange genres (not talking about the mapping feature) to suit they music they listen to.
PS: Props for the current genre management system. Multi-genre tagging is a blessing.