It's a lot of what others have said. The money is a bit hard to come by at first until you find the stash on the left and it's not exactly amazing fun going over there to collect it, die and repeat just so you can going. I'd make every enemy drop $1-2, especially as the enemies are so tough to kill. Let the player become powerful more quickly I'd say. The stamina bar is a good idea, but having to come to a complete stop just to regen it is annoying; and because you can just tap forward and ride your momentum you can mostly ignore it (though I think this is unintentional.
