Prior to viewing the 2000 movie, I read American Psycho about three times. Now that I've seen the film, here are my thoughts.
Let it be known that I love both the novel and the movie, the novel more (as is the norm).
"...there is an idea of a Patrick Bateman, some kind of abstraction, but there is no real me, only an entity, something illusory, and though I can hide my cold gaze and you can shake my hand and feel flesh gripping yours and maybe even sense our lifestyles are probably comparable: I simply am not there. It is hard for me to make sense on any given level. Myself is fabricated, an aberration. I am a noncontingent human being. My personality is sketchy and unformed, my heartlessness goes deep and is persistent. My conscience, my pity, my hopes disappeared a long time ago (probably at Harvard) if they ever did exist. There are no more barriers to cross. All I have in common with the uncontrollable and the insane, the vicious and the evil, all the mayhem I have caused and my utter indifference toward it, I have now surpassed. I still, though, hold on to one single bleak truth: no one is safe, nothing is redeemed. Yet I am blameless. Each model of human behavior must be assumed to have some validity. Is evil something you are? Or is it something you do? My pain is constant and sharp and I do not hope for a better world for anyone. In fact I want my pain to be inflicted on others. I want no one to escape. But even after admitting this - and I have, countless times, in just about every act I've committed - and coming face-to-face with these truths, there is no catharis. I gain no deeper knowledge about myself, no new understanding can be extracted from my telling. There has been no reason for me to tell you any of this. This confession has meant nothing..."
The most striking difference I noticed is the use of the above quote within the two mediums. This is the paragraph in which Bret Easton Ellis delivers the reward you've been working toward. While reading the novel, you have to trek through 376 pages of X-rated satire before Ellis gives you this gift, shows you why you've been crinkling up your nose, choking in disgust, and slogging through entire pages of Bateman prattling on about designer suits and skin-care regimens and Phil Collins. These pages pass through with little introspection from Bateman, and therefore the slivers of reflection near the end are made all the more valuable.
However, in the movie, this essential paragraph is split in half. The first half serves as an introduction, the second serves as a conclusion. As tasty as this is, it is an experience completely apart from that of the novel, where Ellis makes you work for it. The movie comes off as preachier because it ends with lines from this monologue, and the book comes off as less preachy because several chapters follow this portion, the final being "At Harry's." While "At Harry's" serves an essential purpose in the novel's conclusion, it is a caricature of Bateman's yuppie lifestyle instead of a piece of outstanding reflection.