I really didn't like the movie after reading the book, I think you probably did it the right way around. I really loved the first book - the combination of comedy and horror let you read about these awful things while always remembering that this is a comedy, that nothing is really at stake.
The pacing of the first book is really interesting because it started as an online serial before being adapted into a full novel. I'm not sure at what point in the story he stopped serializing it but it does seem to transition from several one off plots into the main plot somewhere around halfway through. I think this was a failing of the second book, which just had one solid plot the whole way through. When concentrated into a single area/plot/mythology, the zaniness of the first book is lost. I hope he writes more short stories about the characters and world, he seems to write much better with that kind of constraint. It's still worth reading though.