Full disclosure: I contributed enough to the crowdfunding site to get invited to the premiere and meet Penn and Teller, so I would have enjoyed the experience even if the movie had been terrible. Luckily, it wasn't.
The plot is pretty original. It's about - surprise - a crowd funded movie. One particular contributor - Herby Blount, played by Penn - donates enough money to hang out on the set and even film with his own hand-held camera. It turns out he's obsessed with Missi Pyle, who, like all the actors, plays herself. He uses his footage together with raw footage he steals from the movie to cobble together his own version of the movie, in which he's the hero. What we're supposedly watching is the director's cut of *that* movie, with his commentary. How meta is that? The result is something of a cross between a classic "movie within a movie" and a "found footage" documentary.
It's really two separate movies. They create a good part of the movie "Knocked Off", a low budget but completely credible slasher/horror movie, and they also create Herby's amateurish additions and edits. During the Q&A, they claimed all of "his" editing and special effects were done with free software that a crazy person really could use.
The acting is quite good. The main characters in the "movie" are Missi Pyle and Harry Hamlin. She in particular does a good job of playing both her role and herself playing her role.
Of course, the whole thing is narrated via Herby's (Penn's) "director's commentary", and that's where all the humor comes in - and it is very funny.
All in all, a quite enjoyable movie.
