Went to see it last night, it was great. He really nails the Tommy impression. I’m not sure how much was embellished for the film but Tommy Wiseau is undoubtedly a fascinatingly odd character.
I’d say you don’t necessarily have to have seen the room to enjoy it but you would miss quite a few of the references in the first half of the film. Once you get the gist of tommy then that is funny without any context.