I withheld a half star because I'm not entirely sure this game is supposed to be beatable, and if it's not, I find that depressing enough to ruin the game for me. Otherwise, this is a pretty good game, except for two things (that are personal preference):
Inability to choose upgrades; just have to count on whatever the game hands me, and
Laser-weapon; I don't like it one bit, I would have rather stuck with the rapid-fire scattershot. I think it cost me the game since it's the final upgrade. It's just not easy to wield, and accuracy actually counts in this game; wasted shots are wasted time.