Needs a few tweaks.
I found that the supposedly 'easy' mode was just as hard as the hard mode, possibly harder. If the enemies spawn all over you can just stay to the left or right to get rid of them, but if they spawn from the sides you have to stay in the middle.
Also, even on hard mode I barely made enough money to get decent upgrades. I got up to level 15 or so after which the game became impossible. There's just too many of them!
Also, the jump feature was useless. Even at the peak of the jump you couldn't avoid getting bitten.
Fun game though, probably about 30 minutes spent playing it.