I've seen the Simpsons movie and read the novel, and like an earlier commenter said, the similarities end there. Like a lot of Stephen King's work, the novel explores the dark side of human nature. Murder, rape, insanity, egotism, religion, thirst for power etc. The Simpsons Movie isn't as bleak and a great deal more gut-busting in a metaphorical sense. I thought both were amazing. The climax especially in the novel is jaw-dropping. Even if the idea isn't totally new, the execution is purely Stephen King.