I'm not one for sub-catergorizing things.......have got my 'Rock' broken down into 3 broad categories.....
Modern Rock would denote stuff like Nickelback, Hinder, Hoobastank etc.
Rock is a general category for my old/older stuff like Bon Jovi & Guns N Roses.....also encompasses classics like Led Zeppelin and Kansas
I use Alternative as sort of a general 'All-Other' classification........I prefer it this way because if someone were to go through it......they could splice it up so many different ways, it wouldn't be funny.........(AFI, Coheed & Cambria, Something Corporate, Good Charlotte, Linkin Park, Story of the Year, Change of Pace are just some of what I would call 'Alternative' artists)
My Genres as a whole run like this though
Electronica & Dance
Rap & Hip Hop
: 1,615 tracks, 9.92158 diversity
You'll buy your first one for what you think it is.....and your second one for what you know it is