When it comes to StarCraft's story lines, I think making Kerrigan the face of the Zerg is the absolute worst decision Blizzard ever made. The lore of how the Zerg communicate as a telepathic hivemind and seeks nothing more than the assimilate the entire galaxy is what I find interesting about them in the original game. Giving the Zerg a human face and goals completely ruins how "alien" the Zerg are meant to be.
Their campaign in the base game culminates in the Overmind invading Aiur because he wants to assimilate the Protoss, but just any spot on Aiur won't do, no no. Instead, you're tasked with destroying a temple made by his grand pappy or whatever so that he can be warped onto its ruins because it considers it Holy Land. That's alien logic, and I find that shit fascinating.
The Brood War expansion is, for the most part, alright. However, any time Kerrigan gets involved, it feels like a StarCraft fanfiction where the writer obviously had a favorite character, and made every other character a complete dumbass for trusting the obvious villain time and time and time again. Kerrigan tricks the Protoss into doing her bidding not once, not twice, but three times over the course of the story, and every single time she back stabs them without fail, and the Protoss act surprised every time she does. All this to make her some generic "galactic alien empress" in the ending.
Kerrigan is fucking boring, and fuck StarCraft 2 for having Raynor giving up the idea of revenge in exchange for being sadbrained because he's "in love" with her.