I would add multiplayer so that another player can control a different paddle.

I would add a scoring system and maybe add some different backgrounds. There was also some strangeness with the movement of the rocket which I would have liked to sort out.

I would add multiple maps and bosses. I would also add more diversity to the map, like torches. I would also add multiplayer, like battles between who can complete a level faster. I think bosses would be pretty easy, as well as multiple maps, but I ran out of time.

If I had more time, I would have increased the number of aliens that spawn after the user kills a certain number.

I just saw a platformer game that could run up the angled platform blocks.  I would have liked to do this because the character in my game gets stuck against the invisible part of the block.

I would make the ball's motion continue after contact with the feet is lost.

Decrease the border width at the edge that prevents the ball from going to the true edge.

I might try to make the enemies more advanced with their movements and make them stop when they reach the player. Also improve the strength of the enemies as you make it farther through the game.

Add a mini map that shows the player the general area they are located in the large map, along with where the keys are in the map