From the standpoint of pure viewing enjoyment, I think last night's edition of The Wire was the best season four has had to offer.
Let me single out the economy of narrative achieved by letting the plot thread about Namond's lieutenant stealing the stash on claiming it had been jacked allow Prop Joe's dilemma at the end to move forward without explication. That sort of internal echoing has always been one of the show's great strengths -- the kids were engaged in a kind of Russian doll version of the grand scheme playing out between Omar, Joe, and the co-op members. Getting Bob Ehrlich to do a cameo is also a pretty sweet touch.
Let me also note that I thought I'd caught the shows writer's in a continuity error. Watching Episode 48, I got confused as to where we were in the calendar. Carcetti had taken office, implying that we were in January 2007, but the narrative seemed to have just skipped over the month of December. Episode 48 further clarified both that Carcetti was no longer mayor-elect and that it was, in fact, still late 2006. Big problem! But then I looked up the Baltimore charter and it states that "The term of Mayor shall commence on the Tuesday next after the first Monday in December succeeding the election and continue for four years and until a successor shall have been elected" so it's all good.