Also, from a little while back, is this collection of crime writers (broadly defined to include Irvine Welsh) singing the show's praises. There are a few spoilers, so if you've not watched it, just make do with this quote from John Williams (the crime writer, not the composer):
Then I watched The Wire. And there was everything I'd liked in the work of Higgins or Leonard or Pelecanos: the inventive dialogue, the characters etched in shades of grey, the prevailing mood of moral ambiguity and profound cynicism as to the motives and efficacy of the forces of law and order. There, in particular, was the sustained attack on the war on drugs - a war that makes the Iraq adventure look well thought out - that neither our newspapers nor our novelists (with the shining exception of Richard Price) seemed able to make. There, in a nutshell, was the revival of American social realism: the Steinbeck/Hammett/Algren tradition that seemed to have been lost in a welter of postmodernism, post-colonialism and pure unadulterated schlock.