Given that Diablo III's (allegedly) right around the corner and WoW's just a race of English-language-butchering kittens away from having the market cornered on cuddly things in MMOs, StarCraft's sort of gotten shoved into the background during this year's BlizzCon.
And that's really a shame, because it's doing some pretty damn awesome stuff.
During BlizzCon's Heart of the Swarm campaign and lore Q&A, Blizzard dropped a few details about the wriggly, pulsate-y expansion's single-player campaign. Most impressively, Zerg units will evolve relative to campaign progress, ultimately giving you choices between "genetic splits."
The example used during the panel involved the tried-and-true, foolishly faithful Zergling and his never-ending struggle against Terran bunkers. One of the two potential split options, however, involved evolving tiny, insect-like wings that allowed the little Zergling that could to climb over terrain and go around the bunkers. Utter obliteration of the Terran base followed shortly after. Another person in the audience said it best, I think, when he obnoxiously shouted "OP!" But I also agreed with the rest of the audience's assessment: "[Awed silence]."
The other split choice, meanwhile, allowed you to triple your Zerglings in the blink of an eye. They were called Swarmlings - and with good reason. I watched with a mix of horror and more horror as the freshly hatched Zerglings devoured an entire marine army in the blink of an eye.
Furthering the campaign's evolution theme, you'll also be able to destroy planets as you see fit. Depending on the planet, your units will gain different permanent stat boosts. For instance, one planet might speed up your mineral harvesting. Another might do the same for gas. It's your call as to what you destroy and what you graciously spare to live an empty existence, paralyzed with fear of your inevitable return.
Also interesting was the panelists' response to a spoilerific audience question involving certain choices you could make during Wings of Liberty's campaign. In short, yes, those choices will carry over via your previous saves or Battle.net. Bear in mind, however, that this isn't Mass Effect. Blizzard explained:
"We are actually planning to bring your choices forward into the game. If you're playing Heart of the Swarm and you didn't finish Wings of Liberty or reach the point where you had to choose between the tunnels or the platform, it goes to the canon choice - in that case, flood the tunnels."
"That said, this is a Zerg campaign, and many of those were very Terran-focused choices. So I can't say that the choice will have a huge impact on that game. But you will hear references to the choices you made in the game.