OK bugger reality + the clichedness.
How about if I add asteroids, which u shoot + they break apart to create more gems.
also limit the players lazers to only onscreen, ok which is a bit stupid since bullets dont disappear as soon as theyre not visable (whats the proverb about that tree in the woods) but it stops the player 'accidently' shooting something they cant see, i.e. aids gameplay.
Also u could have a powerup which the bullets bounce off the screens edge.
Also Now u can rotate the player's spaceship instead of having it fixed horizontally, its starting to resemble the old arcade game asteroids more than defender but shes right.