I'm learning The Poltergeist from Bolcom's Three Ghost Rags right now and I would definitely place it in the 'advanced' category. Not because the notes themselves are so difficult to play, but because there are about 15 accidentals in every measure of the piece, which already has 6 flats to begin with. Makes it rather difficult to memorize and sight read. Oh, as to length it's 10 pages and lasts about 3'45". Unfortunately that is all I know about Bolcom's works...