In my game, you are a ball of light created by an organization to destroy enemy ships, and you are assigned a pretty agent named Ariel to instruct you.

Under ordinary circumstances, as a ball of light, you are vulnerable. But pressing the A key brings a forcefield around yourself for a limited time.

While this forcefield is on, destroying over 1 enemy ship brings a 2x bonus to your score, destroying 3 brings a 3x bonus. When your forcefield ends and has to be "charged", the score multiplier resets to 1x.

Although you can kill enemy ships using your forcefield, something called shockwaves will kill you either way. Shockwaves are waves of energy which come from the side of the screen.

So after destroying 35 enemy ships, the game basically ends. You get a bonus level if you have gone beyond a certain score, which is a sidescrolling minigame where you avoid energy beams while moving.

I also have a couple of boss ships which have forcefields which go up and down, but the game still seems bland to me.

This is a futuristic space game.

My thoughts:

How should I expand on this game?
Is it possible to introduce currency? How would it be used?
Can I diverge from science fiction and give the game a horror-based storyline (say the pretty female dies, or turns out to be a demon)? Or would that just be too much? Would a scary story be a cheap way of spicing up this game?
Do you think I should add a 2-player mode with a Campaign which plays just like the 1-player mode but with two people on-screen, and a Deathmatch mode where two people try to destroy each other using their forcefields?

Why 35 ships? Why not let the player go until they die?

Why 35 ships? Why not let the player go until they die?

That's actually a good point to bring to my attention.

The game is internally crafted in "waves" of enemies which do different things each wave. I thought this sufficient but since I have decided to expand on the game, I can rotate the waves once they end back to the starting wave, increasing the speed (translating to more difficulty) of the enemies each time. Which would create a never-ending experience.

You only have one weapon(forcefield) why not add a second weapon that makes an expanding shockwave around(away from) the player's ship filling up ~1/3 of the screen ?