Original author [Bret Easton] Ellis said, “American Psycho was a book I didn’t think needed to be turned into a movie”, as “the medium of film demands answers”, which would make the book “infinitely less interesting”. He also said that while the book attempted to add ambiguity to the events and to Bateman’s reliability as a narrator, the film appeared to make them completely literal before confusing the issue at the very end.
I don’t really remember it, so I guess it isn’t very memorable. It seems not to have been especially praised by critics, nor by the author. https://en.wikipedia.org/wiki/American_Psycho_(film)#Reception