I allways look up the artist on allmusic.com and READ about the genre.
After many hours of studying I can say I have a pretty good overview of the genres.
I found it best to divide the genre into genre and sub genre.
My genres areGenre:
Blues, Country & Western, Electronica, Hip Hop & Rap, Jazz, Others (comedy, mix etc...), Pop, R&B, Reggae, Rock, Techno & Dance, World
Sub Genre:
Acid Jazz, Alternative Hip Hop, Alternative Metal, Alternative Rock, Ambient, Big Beat, Black Metal, Blues, Britpop, Celebrity Pop, Chillout, Classic Jazz, Classic Rock, Club/Dance, Comedy, Comedy Rock, Country Pop, Dance Pop, Dancehall, Disco, DJ Mix, DownTempo, Easy Listening, Electro-Funk, Electropop, EuroDance, Folk-Rock, Folklore, Funk, Funk-Rock, G-Funk, Glam Rock, Goa Trance, Goth Rock/Metal, Grunge, Hard Rock, Hardcore Hip Hop, Hardcore Rap, Heavy Metal, Hip Hop, Hip Hop Soul, Hit Collections, House, Indie Dance, Indie Rock, Industrial, Industrial Metal, Industrial Rap Metal, Industrial Rock, Mainstream R&B, Metal, Metalcore, Miami Bass, Minneapolis Sound, Modern Rock, Neo Soul, New Jack Swing, Norwegian Hip Hop, Nu Metal, Oldschool Hip Hip, Oldschool R&B, Pop Rock, Post-Rock, Post-Grunge, Prog Rock, Prog Trance, Punk Rock, R&B Pop, R&B Soul, Rap, Rapcore, Reggae, Rockabilly, Soft Rock, Soul, Soundtracks, Southern Rock, Stoner Rock, Tech House, Techno, Trance, Tribal, Trip Hop, Vocal Pop.
Rock is a huge part of my sub genre. 34 of 86 sub genre is part of rock.
With 13 000 tracks, this was a pretty extensive job. But I simply LOVE it now.
I can get auto generated smartlists with the desired genre/subgenre mixed with BPM and intensity.
And with all my tracks rated as well, my life of music is just sweeet
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The most important thing of genre is not to place the artist "correct". It is for you to know the genre
(a little), and place the artists/albums/songs acording to where you feel it belongs.
After all it's your library.
There are no right answers when it comes to genres