a scanner darkly
Faithfully adaptated from Philip K. Dick's novel, Richard Linklater's animated 'A Scanner Darkly' is a grim tale of drug-fueled paranoia. As with most P.K. Dick novels, the story is cloaked as science fiction to extrapolate trends in contemporary society and raise philosophical issues, in this case centered around identity and the loss thereof. To illustrate, the title refers to 1 Corinthians 13:
When I was a child, I spoke as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things. For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.

'A Scanner Darkly' portrays a near-future totalitarian society where large numbers of people are addicted to a drug called Substance D (D for Death). Undercover police detective Bob Arctor (Keanu Reeves) has been living among addicts for so long he has gotten addicted himself. Sharing a house with his equally addicted friends Barris (Robert Downey Jr.) and Luckman (Woody Harrelson), Arctor leads a slacker's existence with Donna (Winona Ryder), a local dealer, providing the only spark in his life. Mostly Arctor and his friends just sit around, have meandering, inane conversations and vent their paranoia in complex schemes.
Arctor is known to his superiors as Agent Fred and reports to them anonymously, in a so-called scramble suit which hides his identity by projecting a continuously changing appearance. When Agent Fred is ordered to spy on Arctor, i.e. on himself, and cameras are installed in the house where he lives, the schizophrenic effects of Substance D become apparent. Instead of realizing the absurdity of the situation, Fred starts observing Arctor as if he was another person.

This is only the start of an increasingly confused and paranoid series of events - which need not be revealed here - ultimately leading to the uncovering of a vast conspiracy. By then the cynical question is whether Arctor has enough braincells left to act upon his discovery. Along the way, though, Arctor has moments of clarity where he muses on his fate:
What does a scanner see? I mean, really see? Into the head? Down into the heart? Does a passive infrared scanner (...) see into me - into us - clearly or darkly? I hope it does (...) see clearly, because I can't any longer these days see into myself. I see only murk. Murk outside; murk inside. I hope, for everyone's sake, the scanners do better. Because if the scanner sees only darkly, the way I myself do, then we are cursed, cursed again and like we have been continually, and we'll wind up dead this way, knowing very little and getting that little fragment wrong too.

However, compared to the novel, which was based on P.K. Dick's own experiences in '60s California drug culture, the film doesn't quite have the same vicious sting to it, for two reasons. One, Reeves in the lead role is just too zombie-like, and even with the occasional voice-over doesn't convey enough of his inner conflict. Reason two is form. Using the same rotoscoping animation technique Linklater pioneered in 'Waking Life' (filming real actors and 'painting' them over to produce a realistic style of animation) seems like a great idea to visualize Dick's weird futurisms and hallucinations (especially the scramble suits), but ends up being a little too cute and polished for its subject matter.
Verdict: recommended as an introduction to the novel, but for a more visceral experience go back to 'Naked Lunch'.
More info on the book and film at PhilipKDick.com.