Nicolas Cage is wonderful as the cracked out and wholly crazed officer. It's the role he was made for, one where all his various tics and mannerisms get worked to the max. He's absolutely marvelous, both appalling and humane, sympathetic, somehow, even when revolting. Eva Mendes also does a good turn as the hooker with the heart of gold. Val Kilmer is a bit dull as the caricaturish evil cop, but he gets very little airtime, so it's ok.
The movie is definitely quite a bit longer than it needs to be, and drags a lot towards the end, but the occasional flights of hallucinatory joyful fantasy go a long way in making up for it. I liked the movie a lot, despite it's being a kind of meta-movie, a commentary on what such movies are like rather than an actual specimen of the genre. The ending I thought was particularly clever in this regard, a nice compromise that allowed Herzog to have his cake and eat it too. So overall, though it was ot a great film, and went on far too long, I definitely liked it quite a lot.