Ok so maybe it's not Rock and Roll but it's a fun movie. I guess it's this generations version of Grease. The lead, Nikki Blonsky is excellent for the role of Tracy and John Travolta steals every scene he's in. If you haven't seen it you should. Even if you don't like musicals it's still a great movie.
I've heard bad things about the one from the 80's such as Edna Turnblad's voice being awful. However, if you, a musician, recommend it I just might rent it
I'm not recommending it as a musician, just a somebody who thinks John Waters can be really funny sometimes, particularly when he's not at his most shocking/disgusting.