Rented this movie with my roommates in college. Fairly early on, the one from India blurts out, "What the fuck are we watching?!" So at least you're not alone in Not Getting It.

I'd say it's about horror-comedy. Tension that could become absurd or horrifying or both. Exemplified in abundance when Christian Bale leaps around a corner with nothing but tennis shoes and a running chainsaw. Message be damned - the film has your attention. And the payoff is watching that chainsaw tumble down a staircase, barely knowing what you want to happen.

That's set against literally bloodless surprises, creating unease by allowing no solid ground. You're watching a movie called Rich Prick Kills People and you've watched this rich prick kill people and you're not one hundred percent sure whether this rich prick actually killed people. There's no spoilery answer because it's not about that.

'Why is this film popular?' is mostly a matter of good acting, good pace, and some extremely memorable bits. Unfortunately the shock value is steeply diminished if you know they're coming... and the best parts became stock references for the 4chan generation.

'Why is this film important?' involves an admittedly shallow discussion of postmodernism. Patrick Bateman is trapped in hyperreality. It is so convincingly artificial that it has subsumed the real world. "Objects have won." He is so deep in the fake-world economics of useless boardroom executive horseshit that even murdering his fellow vice presidents has no impact. The system folds right over it like it never happened. This impotence extends to the sex workers and service workers he tries to lash out at: it does not matter. His most vile and id-crazed fantasies cannot so much as stain a closet.

... and of course there's a fandom of dipshits who think this useless maniac is the coolest guy evarrr.