As a zerg, I don't think the game is as imbalanced as some people say. Far less imbalanced than wings of liberty was, at least. I do think some units are a little too strong though (medivacs!).
Hydras aren't that much stronger, the main thing is now they can retreat and position better. They're still just glass cannons with no health, but with vipers in the mix now I can see them being harder to kill.