I find it ironic that this film, given its subject matter and plot, should cause the amount of controversy it did.
It appears, as an Amazon reviewer also notes, to be a "love it or hate it" kind of film. I have read elsewhere that it changes much from the book, and apparently is nowehere near as good as the book. Well, I'm gonna have to read the book then! (I love it).
Essentially pointing out the madness induced by our obsession with the media, in particular TV and Hollywood, NBK is more than just a story about two cold-blooded killers, also lovers, desensitised by films and tv. It is about how the media obsession affects us all, even those of us who may not realise it. It is about how veryone has a dark side of their psyche, their own personal demon. Let the demon take control, and you turn very definitely bad.
The film is pretty gory, many scenes are obviously intended to shock (and do so). I like the technique used throughout the film whereby every so often the picture changes to be black and white, often merging into trippy scenes (and yes, the two main characters do take drugs although you aren't properly made aware of this except for one brief shot during one scene). The different style used in the flashback of how the two characters met is a good sendup of classic sitcom style.
The final few scenes are a glorious chaotic bloodbath that abruptly tails off to the very last scene - the film has a number of smaller such "spikes" of violence (not least of which is near the start). Throughout the film we are also reminded that when they're not killing people indiscriminately, the two killers are just like a normal pair of lovers. They have some arguments, they're a little simple but not stupid (in fact Mickey shows his true intelligence during the interview).