Since I have expressed my thoughts on the first installment, I figured that it is time to talk about the Zerg. It's something that you need to talk to your kids about. Though they might have thoughts about experimenting with them, Zerg are very dangerous. While Zerg abuse is not a top killer, once addicted, the subject's fate is certain.
Heart of the Swarm is the second installment/first expansion of StarCraft 2. Personally, I think it has one of the best game acronyms of all time: HOTS. The single player campaign almost exclusively focuses on the Zerg. In one mission, you command the Hyperion, the ship Raynor used to command.
So after the magical space fairy turned back time at the end of last time, Sarah Kerrigan is human. The entire campaign is sort of an abstract replay from the Zerg campaign in the original StarCraft. Raynor disappears pretty quickly, then Kerrigan turns into the Queen of Blades again. Things quickly sprial out of control, except that Mengsk dies.
Female power advocates should be quite happy with the Zerg, as 90% or so of Zerg upper management are women. Kerrigan is on the field and controllable in nearly every mission. Between missions, you can switch her abilities. There is a twist to regular units, in that occasionally, you can choose between two different upgrades that are permanent, but three or so others that you can switch around with.
The campaign structure is semi-nonlinear, in that you choose to go to one of two places, then spend a few missions doing things there. Overall, I didn't find the story that intriguing. There was a little bit of suspense, but it wasn't that great, and I don't react much to such things.
I haven't played around much with the Zerg much at all in StarCraft 2. Once, I started getting harassed by dark templar, who are invisible without the aid of detector units. Since I'm playing Zerg, there isn't a problem, because that's what overlords do, and Zerg have plenty of those just hanging around. Except StarCraft 2 changes that, and overlords no longer detect. I am wondering why I was not informed of this little oversight, and why the campaign never said anything about it.
Bottom line is that if you like StarCraft, there are far worse things you could be spending money on, so get HOTS.