Very good reaction at the initial game play, love the game art, it really is funny. I think the buttons could use some hover action. Also, as most people stated here, upgrades need to give more impact!! You just feel like you work too much for too little. Why can't the health be a permanent boost? As well as the other upgrade.
Well, I am having fun though.. but I get desperate very quickly..
 "Tower of Salvation"){kind=icon}
 "Sheep Happens"){kind=icon}