House have subgenres like acid or classic in my collection. those are saved in the "style" tag.

other examples of fields i am using: venue (e.g: club, beach, warehouse, home), set time (e.g.: warmup, peak hour, afterhours), mood (e.g.: heavy, bouncy, druggy, dark, jackin), vocals (male dialog, female singing, none)

as its not the best idea to manually add all additional fields the user have it would be an idea to give to user the option to manually add own additional fields.