First off – the movie is to Fantasy as Paul is to SF – meaning the better versed you are in Fantasy films and the Fantasy genre overall the better time you will have at the film, as you will get more of the in-jokes. Secondly, McBride, Franco and David Gordon Green (the director) had previously starred together in Pineapple Express, so if you’ve seen that one, you’ll have a pretty good idea at the sense of humour in the film.
Secondly – this movie is not for kids – not only are the references likely to go over their heads, but there is a lot of violence, nudity and references to various bodily fluids.
Finally – this movie is a lot of fun. Knowing I was going into a crude, rude send-up of the Fantasy genre, I can say I was totally impressed, and more than a few times a little surprised, and once shocked at what some people will do if you let them have a muppet in their film.