The critics love it because it's pretty unique and atypical, beside having great acting and writing. It doesn't seem to have the kind of mass appeal at home it enjoys in some countries, though. It's not always a very nice mirror, for one thing, and it's very slow-paced and introspective for American TV viewers (who prefers entertainment even in drama).

It has a lot of criticial and in some places mass appeal in part because this sort of slow going character driven social drama is more popular in many countries than it is in the US, and of course it is well written, has great acting and it's not shallow. It also has bigger means to recreate the era than TV gets in most countries for this sort of show. It's also set in a fascinating time of great social changes and the beginning of a decline for America. The interest of the American own critical perspective on this period is a big part of the show's appeal (auto criticism is something Americans do well, when they do).

They lose points for their bad depiction of Québecois of the mid-60s, though. Megan and her parents are just not credible - way too European in their mores and thinking. Not quite sure why they made her a Montrealer instead of French, since they obviously wanted that contrast in the mentalities. In those years Québécois still found the Americans way too liberal. It was about to change, but it's too early for a Megan to be credible.