A worthy expansion,
Verified Purchase(What is this?)
This review is from: Starcraft II: Heart of the Swarm (PC/Mac DVD) (DVD-ROM)
Although expensive for an expansion pack, the Heart of the Swarm campaign has as much new single player content as the original game. The missions are interesting and varied, and the strong story is conveyed with a good number of cinematic sequences, which change slightly to reflect choices you make in the game. The difficulty bar is set a little lower, so you will probably want to play on at least "Hard" mode if you are looking for any kind of challenge.
I don't play much multi-player (because I suck) but I suspect that if you where only interested in that aspect of the game, you would consider the few additional units to not be worth the price of admission.