I really like the concept of adding features to a basic game to show how features can change a game. We went for a similiar idea in that regard.
The game felt easy at first, but become more challenging as you added features. The art style is basic and lacks a bit of character, for example I don't think that the player and the enemies should look the same. As a sound design guy I noticed the shoot effect is also very basic and the music feels uninteresting. There is also an ambient background track missing that could have added some atmsosphere. Try to bring more variety to sounds next time. As you really nailed the theme I think it's still a good piece of work. Keep it up! : ) /alex