Nearly everyone has their own definition of the word 'good'. Maybe you won't enjoy it (I, for one, don't know if I'll like the music. I don't know most of the contributing bands), but many people will. Hopefully we'll both enjoy the movie, whether the music suits our tastes or not.
Did you listen to any of the 5 released songs yet, or are you basing your opinion on past works/your image of the bands? Personally, I think even though most of the bands are rather unknown, what I've heard of the music has been completely spot-on and awesome.