great work- a lot went into this obviously.
-I didnt like the limited visibility on the sky above because guys would fall down onto me without any notice and kill me-
-In the buy screen, It took a while to realize I had to arrow over and spacebar to buy instead of clicking
-in the buy screen when you try to buy something but dont have enough money- the text field that displays the cost is behind the "cost:" text after its animation
-Id suggest coloring money and pickups something other than black so you can see them and its more obvious you can pick them up
a lot of attention to detail here- maybe team up with an artist / animator and this game could be pretty rad. nice work