Well, I beat it. About 4 days in and a total of 8 hours or so. Heart of the Swarm had a nice variety of missions, although there weren’t that many. Most of the missions expanded as you progressed so they weren’t simple and quick. I don’t care for timed missions though and it seemed they crammed an awful lot of them in there.
I forewarn you, this is the ending of the game. As with all Blizzard cinematics, it’s awesome: