Yup, 4.
*spoiler*
I probably got as emotional (not sad, believe me) when Gus first came out of Salamanca's room following the blast. I was like noooooooooooooo...yeahhhhhhhhhhhhhh! Fuck that psycopath.
So there's going to be season five? My pick: the German company which ( I believe) owned Gus' operation sucks Walt/Jesse in. At the same time, the DEA starts to investigate them. Although, tbh, they could leave the story here and I would be more than satisfied. I'd hate for it to stop its exponential rise by the season because they have to start making less believeable story lines. That is one of the key strengths of the show imo, its 100% believable (although Ted's death was a tad convinient & pretty contrived relative to the rest of the show).
Fuck I love it.