You're thinking of season 4, that's the one with the schoold kids. I think that's greatest season too but I also love season 2. A lot of people seem to not like it as much because it moves away from the street gangs a bit but I thought it was necessary so as to establish the show as more than just a cop show. Season 2 is about a lot more than dock workers, its about the death of the American working class to a certain degree. I was also really drawn into Frank Sobotka's arc (Chris Bauer was terrific and should have received an Emmy nomination as should have many other actors on the show across its 5 seasons, shame he's pretty much wasted on True Blood) and though their arc moved at slower pace I enjoyed the Barksdale story and felt like this was the season where Stringer Bell came into his own as a truly amazing character (and my favorite on the show).
Such a shame so few people watched this show while it was on, I'm part of the guilty party unfortunately, but at least now its starting to get recognition outside of its original fanbase and the critics for the great show it is. I love quite a few HBO dramas but The Wire puts them all to shame (including The Sopranos, great as that series is).