Is it just me, or are Stalkers the end all unit? Blink, shoot air, ground, good damage, moderate health, seem fairly cheap (I don't know the cost but Protoss seem to make a lot of them). Murauders are also like Stalkers, good at everything except I think they just strictly better at fighting. They deal bonus damage against mechanical which is great against protoss, and they slow units with their attacks, which is great against Zealots/Zerglings. I know that in Starcraft you could win games using only Zealots and Dragoons, but I'd prefer if their was a lot of unit mixture.
Zerg are just really screwed up at the moment so it's impossible to tell what's good/balanced with them. The only thing I can say for sure is Zerglings own Stalkers if they have no backup/zealots.