This is good, silly fun, the kind of story in which the main characters bicker over a walkie-talkie about what to call their plan (Operation: Catastrophe vs. Operation: Piggyback, both puns) even while running and being shot at by marauding alien monsters. And the evil alien monsters love fighting and musical theater, and "fought one another in a three-hundred-year-old civil war that is believed to have started over a parking space." You know, the kind of goofy, off-the-wall humor that many kids think is just hilarious.
Illustrated with a few comic strips (could have used more of those) and other drawings, the book bogs down in places, and would have benefitted from a firmer editorial hand: lopping off about 150 pages would have done the story no harm and done more to hold the interests of the kind of kids who will be drawn to something like this. Still, this will be a popular choice for fans of Terry Pratchett and Larry Gonick, and, with its abundance of strange creatures, whacky scenes, and silly accents and voices, it should make a great read-aloud.