Just thought I'd pop in here and inform anyone wishing to buy Heart of the Swarm for the single player:
The campaign in this game is nothing but an afterthought, it's just an intro to the multiplayer. If you don't want to play multiplayer you have no reason to buy this game.
The story has the most embarrassingly bad writing and cringe-inducing dialogue you'll ever see in a video game, even surpassing Diablo 3.
But maybe you don't care about the story? Maybe you just care about the gameplay? Well you're still out of luck because the campaign has little to do with true RTS, every single mission is a race against the clock, it's all about rushing (as I said, it's an intro to the multiplayer). All the fun of base building, defense, tactics are gone. Here is how every mission plays out: You have masses of FREE and UNLIMITED units that respawn at your base whenever they die, and you are given xx minutes to beat the mission or you will lose, and all you'll actually do is select the units and press 'A' at the other side of the map.
tl;dr: Campaign story is boring, lame, and without unexpected turns; gameplay is hectic and repetitive. HotS is for multiplayer only.