The Lem's novel has nothing to do with this movie. It is a deeply philosophical piece even surprising for a young man he was while writing this novel. Of course, a person such as Lem matures quickly during the war. I agree that the movie is dull - too bad it's come to be closely associated with the novel by many people who either don't read much or don't have access to a good translation. Contrary to the movie, the mental ward and its patients in the novel are not the main topic - it is an illustration to the madness of the humanity in general. The novel might be considered as a dialog of the author with himself, which is typical for Lem: his characters are often imbued with his own personality.
Review of Hospital of the Transfiguration
