Where to start?
Based on the novel of the same name by Philip K. Dick, A Scanner Darkly stars Keanu Reeves, Pre-Iron Man Robert Downey Jr., Woody Harrolsen, Winona Ryder, and Rory Cochrane (who plays the funnest role of a paranoid hallucinating drug addict).
What makes the movie amazing is the rotoscoped technique used to make it animated, yet look exactly like the actors. Most of the scenes were shot using the actors, and then sent through a vectorizing graphics effect created specifically for the movie, creating a wonderful Flash-animated style similar to the amazing 2008 animated documentary Waltz with Bashir.
A Scanner Darkly is explained on the Wikipedia page synopsis:
The film tells the story of identity and deception in a near-future dystopia constantly under intrusive high-technology police surveillance in the midst of a drug addiction epidemic.
5 stars out of 5
Original Post title: FFOTD: A Scanner Darkly