I just finished watching the final episode of the fifth and final season and the whole thing is amazing. I'm not exaggerating here when I say it's the best thing I've seen on T.V. It's just brilliant storytelling. It's so layered and rich and realistic - granted I've never worked for the police, in the drug trade, down at docks, in inner city schools, as a politician or at a newspaper (although I did have a paper route when I was eleven), so maybe I don't know if they actually got those things right. But I do know that it's like nothing else I've seen and it feels realistic, and I'm not talking about the camera work here. The stories, the characters, the frustration, the day to day, it all feels...familiar. I really can't say enough about it. Seriously, I feel like if you watched this series and then told me you didn't like it, I'd honestly have to re-consider our friendship.
You can read more about the series in this New Yorker article (among other places I'm sure), but I'm warning you, if you haven't watched the full series yet there are some plot points given away - I read this article before I finished season three and was not pleased to be told the fate of some characters. So on second thought, forget the articles and just go buy, borrow or steal this series.
It's worth it.