This game really needs an upgrade system in order to make this a fantastic game. The game as it is now, its highly based on luck, and its just a little too basic for someone to care enough to play for the amount of time it would take yo get lucky enough to win.
You are supposed to test a game for playability before you upload it. You also need to take into account that the player wont know what I'm assuming is zero room for error when choosing upgrades. Anyway, the excruciatingly slow turret renders this game unplayable. The starting speed should be doubled.
Its pretty clear that the only people that rate this low, are too young to realize this was the first type if game like this, and can't appreciate its value.