It's so deliberately vague and emotionally thin that it makes it too easy for the audience to project a deeper meaning upon it. I'm not calling Mad Men (or Inception, for that matter**) shallow - rather than nowhere near as declarative as Breaking Bad. It's a pulpy show that wants to be immensely watchable and, in that effort, it's succeeds tremendously. The wonderful thing about it is that, for all that pulp, it still creates an emotional resonance that Mad Men has yet to touch***
Spoils for BB and Mad Men:
I disagree with this.
What is deliberately vague about Mad Men?
I would argue that the characters are much more fleshed out and realistically developed on Mad Men than on Breaking Bad. Sure Breaking Bad is more "pulpy," in the sense that it deals with drugs and people, at any moment, can be killed on the show. Mad Men doesn't have that kind of action (unless you consider lawn mower accidents), but thats not what the show is all about. If you want people getting whacked go watch The Sopranos (I like to say that the sopranos was Mad Men with the constant possibility of someone being murdered). Mad Men is about the characters who work in advertising in the 60s, and they are damn good characters. Better than Breaking Bad's I'd say. For example:
Don VS Walt: Don Draper is a bad person in a shiny wrapper. But over the past few seasons we've watched that wrapper be peeled off him. At first it was hard not to like him despite his lies and infidelities, but now we've watched everything catch up to him. We've been along for the ride as he slowly deteriorates into the pathetic drunk he is this season. Every realization (meaning every new lie we realized he was living) we had in the first 2 seasons we watched him pay for in three and now four. Now he's alone and struggling to keep up with the massive change thats taking place in the 60s (which is something I'm not really touching on here but 1960s NY is also a cooler setting than NM). I have no idea whats going to happen to Don, but I'll continue to enjoy watching his ups and downs. Its been a logical path for Don this whole time. From that moment in the pilot that we realized he had a house/wife/kids we've just watched his web of lies unravel and destroy him, and its been a treat.
Walt, on the other hand, has been down a bit more unbelievable road. Breaking Bad is, as you mentioned, pulpy...so I'm a little more willing to accept things for the sake of entertainment. However, what began as very interesting (his decision to cook to support his family in his dying days) has turned to a more generic idea (greed, with cancer very much on the back burner). Walt is no doubt a terrible person, but its a more predictable greek tragedy type of way. Greed is his flaw. It used to be that he made the decision to cook meth, a very poor decision indeed, and now we'll see how that decision ruins his life. But now its been elevated into a more generic (and scarface-y) "greedy" place where nothings enough unless he's a drug czar and he doesn't care what he has to do to get there. In my opinion that strays from the more real, more harsh places his character was developed in the first and some of the second season. We all have predictions as to where Walt's character is going...he's going to go after Gus and try to take over his business, then as a result of his greed get caught and go down. Maybe Vince Gilligan has something completely different in mind, but what I'm getting at is I have no idea whats going to happen to Don Draper. His character isn't following a path I'm familiar with. At the core of his psychology Don mostly just wants to bury the past, but as much as he tries he can't. It comes through in alcoholism, infidelity, and a general lack of a conscience. Walt's just become greedy because he's developed a taste for action/money.
I'm working on a larger response with things like Skyler VS Betty (I think Skyler is mostly there to serve Walt's story like: Will she find out he has cancer?? will she find out he's cooking meth?? Oh now she's divorcing him, but wait now will she join him??) Jesse VS Betty, Hank VS Whoever... but its getting late and I've gotta work tomorrow.
I love both shows, but I called Breaking Bad my second favorite show on TV for a reason, and that reason is Mad Men. They're both better than everything else on TV but I think Mad Men goes for substance/character development where Breaking Bad sacrifices those slightly for pulp/shock. Mad Men's just more my style I guess.