It stars and was directed by Mark Hamill, and he decided to hire a cast entirely of cartoon voice over actors. So you've got Billy West, Jess Harnell, Tom Kenny, Roger Rose, and bunches of others, including small parts for Jim Cummings, Kevin Michael Richardson, Debby Derryberry and ... well, a lot of people. They did most of the shooting during the course of the 2002 San Diego ComicCon, armed with just a basic outline -- ad-libbing the actual dialogue. Apparently they shot more than 100 hours of material. Certainly, the deleted scenes last longer than the film itself. Easter Eggs include a long segment of Harnell and West writing a song for the movie. Special features include a long panel at ComicCon with the cast and other voiceover artists, including Rob Paulsen, Maurice LaMarche and Gary Owens. Jess tells his DisneyWorld story, in a longer form than I heard him say on a radio show. And of course everybody does some of their voices in it.
Non-voiceover people in the movie run the gamut of the comic book world, from Stan Lee to Kevin Smith to Hugh Hefner. There's even a scene with Sid Caesar and Jonathan Winters -- their first team-up since It's A Mad, Mad, Mad, Mad World. In the commentary, Billy West says it's one of the highlights of his life to be insulted by Jonathan Winters (since the scene was ad-libbed). The commentary features Hamill, West, Harnell, Rose and the two heads of Creative Light Entertainment, Scott Zakarin and Eric Mittleman.
Even as someone who isn't big into comic books, I found the movie to be quite enjoyable. As Hamill puts it, it's a movie about fans, for fans, by a fan (a huge comics collector he is -- in the commentary he mentions that he brought in some of his own collection for use as props but wasn't allowed to use them because there was no way they'd be able to cover the insurance). The plot is about a movie studio preparing to launch (at ComicCon) a new project based on a classic comic book, but "revamped" and "brought up to date" -- which of course doesn't sit well with their creative consultant, a comic store owner from Wisconsin who is seen as the world's best expert on the classic comic book.
Anyway, any fan of comics or cartoons should buy this. I got it for $19.99 from a Sam Goody.