A Scanner Darkly is an adaptation of Philip K Dick's novel, and it's all about drugs and their effect on the characters.
It's quite a surreal tale that takes a little concentration to get your head around, but it's an interesting film to watch, with some very entertaining dialogue. Nicely paranoid, the film certainly gives your brain something to do, and plenty to think about.
Of course, I say paranoid, but the constant surveillance in Dick's near-future society perhaps isn't that far off, and the disintegrating consciousness of the 'hero' - caused by his use of fictional drug Substance D - gives us a creative window into his world. It's all helped along by the slightly wonky rotoscoped visuals.
If you give the film a chance it is worth watching.