I liked A Scanner Darkly quite a bit. It's a compelling and entertaining adaptation of the novel A Scanner Darkly by the great Philip K. Dick.
The only real weak spot for me was Winona Ryder's performance as Donna/Audrey. Yes, I thought Keanu Reeves was just great.
This review by Gene Seymour seems to say most of what I'd say, if I were in a writing state, which I'm apparently not in right now.
That said, I am going to waste everyone's time with one of those lame issues that only I bother with. The animated breasts. They're the only real thing in the movie that was obviously not rotoscoped, but simply drawn on the computer. They don't look or move like real breasts, but like cartoon breasts. They didn't have the shine and texture of the rest of the movie.
This just seems like as perfect an example as one could imagine of a movie where a body double would have worked just fine. Take the two shots and blend them together with the magical computer animation.
But I acknowledge that's a minor nitpick and I did find the movie quite worthwhile and smart and a solid adaptation of the novel.