I don't want to be rude, but you have a lot to learn about games and game development.
To begin with, teach the player which objects are bad, what is the blue thingy and what are the green ones.
I'm not talking about some lame tutorial of sort "Hey you can move with arrow keys!", I'm talking about showing the player what everything does, whether it would be some scripted even where bullets destroy something or the enemies leave some sort of specific trace (it is up to you).
I like what you did for the time frame, but you could do better.

You got the core mechanics of a good R-Type style shooter. Now you can first make the graphics be consistent, i.e. make the different objects all have the same graphics-style. Then polish the game. Also when using arrows to move, you should be able to shoot with SPACE or ENTER, not only with mouse.