Got to stage 11 on the first try.
I must agree with the others that it really feels so simplistic yet very enjoyable for a short play through.
The only point of criticism that I can come with is that the buying/selling/production and generally math related rates in the game are a bit confusing when the game is starting to go fast, since on the first easy levels where enemies don't attack you, you really can get by without using the shop. So as soon as you need to use it, it's a bit too late to figure out how it works properly and you are just winging it. But that is solved with couple of play through when you get into the game more. I guess a tutorial in a form of forcing the player to use the shop in the beginning of the game when enemies don't attack could be a natural solution for that.
Not saying anything needs to be changed, just what stood out and maybe a point to consider for future developments to make your games even better :) Overall, the level of originality is amazing and the gameplay when grasped better over few playthroughs (which is not an issue as the game is short) make the game very good!