I think the movie is pretty funny and have watched it a few times now. The music is pretty decent, and it's also a good way to study some Japanese that you won't learn in any textbook.
Though I may talk about some of DMC's songs sometime, my favorite track from this movie is actually by another fictional band called Kintama Girls (金玉ガールズ). In the film, Kintama Girls is only shown in one scene where they are playing against DMC (Battle of the Bands style) at some club. They are singing this ridiculous song called "Detarame Mothercon Cherryboy."
Just so you can get an idea of the colorfulness of the movie and the music in particular (the dialogue itself is pretty tame in most cases), let me explain a few key words here:
金玉 (kintama) - you can see that the kanji is "golden jewels" or "golden balls." Yes, it refers to specific male anatomy.
出鱈目 (detarame) - "bullshit," basically.
マザコン (mothercon) - the tamer meaning is "mama's boy," but it can also mean Oedipus complex.
チェリーボイー (cherry boy) - a male virgin.
去勢 (kyosei) - found in the main chorus (きょせい、きょせいせよ！) - castration.
Silly and crude but pretty fun, I think. Incidentally, the lead member of the Kintama Girls, Nina, is played by Minami Hirase, who also appeared in Battle Royale.