Thank you for submitting the game! Overall I think you did an excellent job of keeping the game small, yet playable. I can see that you addressed many design issues, for example, the number of colors, the speed of the enemies, the size of the enemies, the speed of the player, and making enemies block bullets of the wrong color; all of these interesting design decisions have been packed neatly into a playable game.
However, there are some areas that can be improved. The background is plain white, which doesn't really mix with the pixel art of the objects in the game. The enemies had very nice dithering, but aesthetically it does not mix with the background and the player sprite. The most glaring problem is the lack of an ending. A simple textbox saying "You Lose", would have sufficed. Its a shame this game ends so anticlimactically.
That aside, the game has a simple and interesting foundation that seems to have been executed very well. I look forward to seeing what you can make with less restrictions and more experience.