I’m also in the camp of loving The Wire. It took me a few episodes–it wasn’t until D’Angelo gave the chess lesson that I was fully converted.
My boyfriend and I ordered HBO so we could finally watch this season in real time. We Netflixed the first 3 (and then went and bought them anyway) and had someone tape season 4 for us (which we’ll be buying shortly).
In the commentary for the final episode of season 4, he said that he told HBO that the Marlo story arch would take two seasons. This was when he was pitching season 4. HBO told him that as long as season 4 was good, he wouldn’t have to worry about season 5. Other than that, each season had to be renewed.