As a fan of the books, I applaud Chase Williamson and Rob Mayes for nailing my interpretation of the characters spot on. I would have actually enjoyed seeing them play out some of the more outstanding and righteously entertaining scenes from the book though. I'm a little disappointed at how mangled the adaption is, but in and of itself I think it holds its own. It needed more time and a bigger budget to really have the same weight and presence as the book, but then again I'm not sure anything really could have portrayed this modern-day masterpiece on film and still do it all due justice.
Overall though, I'd just as soon go read the book again rather than rewatch this. It isn't awful by a long shot, but neither is it as fantastic as some of the other reviews are raving. It's a decent B horror flick. The movie is too rushed and the omission, renaming and mishmashing of characters from the book reaaaaaally takes away from it over all. I can't really believe that more people aren't disappointed by this. The book explores some incredible concepts and propositions to think about that are only briefly alluded to in the film. This caused several comments to have sketchy context and created a sense of things not being tidied up and settled by the credits.
tl;dr: Book was fantastic. GO BUY IT AND READ IT RIGHT NOW SO YOU'LL BE READY WHEN THEY SHOW UP. Movie not so much, but still entertaining. Don't watch it expecting a technicolor, holographic psycho disco-haunted house or anything else equally absurd. Watch it with the understanding that it's a compressed and distorted version of the book that still offers laughs but maybe not so many shivers.