I feel like everything that has happened up until this point in the show, was planned out and plotted for from the opening of season 1. Everything just feels that tight and cohesive.
I believe I read somewhere that Vince Gilligan has had a loose idea where he wanted the show to end up, but it took on a life of it's own around the start of the second season because
Despite that though, Season 2 was actually the most tightly planned.