The most amazing aspect of this series is its pace, I never felt the show was running too fast or too slow and it never strays from realism.
The issues that are dealt with are far more than the typical "crime drama"; it portrays a society at large - the education system, the political system that at times can be self-serving for a select few along with the societal consequences from the actions of these bureaucracies and of course the plague of drugs in the society.
Memorable characters, and some truly outstanding actors.
In the end... Everything repeats itself.
David Simon created a masterpiece. Telling a story just doesn't get any better.