The Sopranos

This is The Godfather of TV series. I've rewatched all 86 episodes a few times and it's quite amazing how they'd kept up the quality over so many episodes. Aside from the great acting and writing, the directing is incredible - there are many scenes where nothing special happens, yet the atmosphere makes these scenes unforgettable. Character development at its best: I felt like I was there, experiencing their world throughout the series. A masterpiece.