I feel compelled to do a blog on this film to advise you NOT to go to it. Admittedly it's not my type of film anyway, but that aside, it left no lasting impression, which to me is even worse than strong dislike.
The basic plot is about a 'bad' (very bad) cop hunting down a murderer while battling with his own inner demons. Winding up with an injured back for life, he becomes addicted to drugs, not only for medicinal purposes. While fighting for a serial killing drug lord, he comes down heavy on minor offenders, treating them brutally to acquire their stash of drugs, which he shares with occasional lover, prostitute Frankie (Eva Mendes). Some scenes are completely overdone, ie where he holds two old ladies up, cutting off the oxygen supply of one to virtual death.
The only vaguely interesting thing in the film were the images of the iguanas and alligators, often accompanied by blaring music. I liked them from an artistic standpoint. While I'm sure director Werner Herzog intended them to be symbols of some great truth, it was lost on me...
...Like most of the film. It was devoid of depth and credibility, and the overriding feeling I got from it was: Life is crap. How depressing!