I ordered this not long after I bought and saw Season 1 ... and love both.
This has the usual Matthew Weiner touches, for which he is understandably lauded: the attention to period detail (well, except for some 21st century linguistic slip-ups); the subtle emotions, even when the chips are down; and the well drawn characters.
There are more revelations about Don Draper, and Betty heads for a meltdown, partially as a result of being left out of his true life. That was a way for a marriage to implode back then, and applies equally well now. (Even if identity checks and so on make secret lives less likely to occur, people will always find ways to hide the real them.)
The one quibble I have with the series is that everyone is so mannered - surely some people broke the rules, and not just while drunk. It still makes for excellently nuanced drama - but perhaps not as close to reality as Weiner might wish.