Most of the people that have seen it, will not have anything bad to say about the performances of the leading actors. Yet, it is obvious that Foster cannot sing, and that O'Toole is being Bela Lugosi, the star of the early Dracula films.
Nevertheless, it is not their fault if in the late seventies they were asked to star in such a tremendously average and weak movie about a young rock star in the making whose mentor is a tough Hungarian and former musical star. Eventually, the 50 year old becomes romantically involved with the 22 year old, and I hate the way in all these movies in the end they actually do 'make it' as they say in the film, but there is never just a strong admiration or platonic love. It would have kept O'Toole's character interesting, before it too crumbles down and becomes a sad little human being.
Anyways, it's free on youtube somewhere so check it out there, though mind you, you could be bored to hell with, particularly every time O'Toole is away from the action.