I thought this was very well put, from a reader (Some spoliers):

Jonah,
I agree with you about this season of Mad Men. I don’t think this is a case of the writers running dry though. These are mostly ex-Sopranos guys, and in much the same fashion of that show, Mad Men has a tendency to buck story in favor of staring into ambiguous voids of nothing as if they’re being profound. I too liked the tractor accident — an incredibly well shot and dramatic scene — but I think it’s a bad sign that the show will continue follow these narrative patterns. They’ve been nibbling around the edges of a conflict between the company and it’s new British owners (much like all the potential mob wars in Sopranos), but the conflict stays at a state of unease, never building or going any where…. and then BAM, some startling random moment like the tractor accident completely reshuffles the deck. I hope I’m wrong, but I doubt the tractor will be a plot twist that pushes the story forward, but is instead a device that undercuts and reshuffles the conflict that had been developing ever so slowly.
Did they not know what to do with the Sterling Cooper’s new owners, or did they think it’d be interesting and never intended some over reaching arch that would drive the season? My guess is that it was the latter.
The first season rocked because it had great story arc. The mystery of who is Don Draper, and will he be discovered? Peggy’s struggle to become more than just another secretarial sex object is thrown for loop when she falls for Cambell and gets pregnant. I don’t think story lines like this will return to the show any time in the near future.