The game is very balanced as is, don't get me wrong! But Zerg is kinda... boring, in comparison to some of the neatness that's been given to Terran and Protoss. And Spawn Larva is kinda poorly implemented. You're on a constant 25 second timer that you have to keep up with or you will be missing out on advantages.
At least with the Terran and Protoss if you forget to do their usual stuff (Mules and Chronoboost), you're not totally shooting yourself in the foot. Sometimes it would make sense sometimes to save up energy for clutch situations or, in the case of Terran, you have other abilities that are very useful.
With the Queen, you're pretty much doing nothing but Spawn Larva, and you want to do it ASAP EVERY time. Spawn Creep Tumor is used once at most, and Transfusion not at all.
And Roaches are way to boring to also be the games most cost effective unit. And Infestors aren't as neat as Defilers. And Ultralisks are still under used.
I still main Zerg.