Just finished watching this yesterday. I wasn't convinced for quite a while (first two series apart from a few good eps) but I felt it picked up a lot from S3 and the political angle added quite a bit.
Lester Freamon is probably my favourite character, one of those dogged intelligence backroom types that works methodically and gets results but occasionally comes out of his shell (when drunk, or an audacious ploy).
To be fair looking back over the show as a whole there are a LOT of good characters. I think early on it can be hard to follow because they throw too many characters at you and it hard to work out quite who is who to begin with (especially while you get to grips with the street lingo). But in the long term the benefit is you had a lot of well rounded, developed characters rather than pantomime villains. Not many shows would invest that much time in people like, I dunno, Bubbles, Naimond etc.
Perhaps the beauty is that when it comes to 'villains' (often much deeper than that), there are many from all walks of life:
-The predictable guys in the game (kingpins like Stringer, Avon, Marlo, etc)
-Politicians (sheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeet!)
-Police brass
-Family upbringing
-Glory-hunting newspapermen
etc
....and yet many of these 'villains' are also proper 3-dimensional characters that you can empathsise with at least on some level. Lots of shows do that but not on this scale, you get shows where there are some well developed major villains but not too many that tackle so many different angles at once.
The irony is in fact that while McNulty is kinda the 'main' character in terms of being the poster boy you see on covers, with a heavy focus at the beginning and end, overall the show has a much wider scope and could easily stand on two feet without him.
Anyways, kinda feels like I should give S1 another pass sometime.