You have some good ideas and some bad ones in this game. Here are the things I think should be removed:
* The minimap blocking your view.
* Having less control over your zombies, meaning it's impossible to dodge projectiles, especially the molotovs/whatever is thrown at your horde that instantly kills all of it.
* Not much feedback when you attack a human (There should be a louder sound effect and maybe screen shake)/
Here's what I do like:
* The time limit forcing you to act quickly, therefore making each situation more tense
* Having different enemies turn into different zombies.
* Having the zombies not fully follow your directions to simulate realism (though this clashes with the gameplay because it makes it impossible to dodge projectiles).
I like the idea that having a bigger horde takes away your control, but this can make it impossible to control the horde, instead of your idea of making it more difficult.
You have a good concept, and I think that with a few changes it can become much more intuitive and enjoyable.