Ammos make you bigger and slower. Use them and you'll get smaller and quicker.
There's no number or HUD, pay attention to the blue and green stuff.
You get a score at the end. The higher it is, the better you are.

That's it. You should get the rest by playing.

If you're stuck, gently smash your keyboard. For real. It works.

Controls :
* movement : Z/W/Up, Q/A/Left, S/Down, D/Right
* aim/shoot : Mouse

Ludum Dare #26 48h compo entry.