Lots of room for improvement:
1) enemies are too hard to see due to their small size.
2A) Play field is too small to maneuver effectively.
2B) The gun with only the spread shot upgrade is so powerful there is no need to move about
3)Bosses were incredibly easy with little to no variation between them.
4)Upgrades were too few and over-powered.
5) actual game length was fairly short. about 3 minutes to beat the entire game.
1)Music loop was too repetitive
2)Voice over was too loud and very jarring compared to the rest of the game. If you make another in this style, I'd suggest taking it out and replacing it with some text placed conveniently out of the gamespace