Pros: Addictive gameplay, Good replay value
Cons: Some bugs (Timer will read 1:1 instead of 1:01 etc..., Restarting the game doesn't reset bullets)
Suggestions(One for each category that would of taken it to the next star):
Better difficulty curve (I think I could play forever etc...)
Bug fixes
Music / more sfx
Animations for the enemies.
Additional collectables for more points (possibly bonus drop when enemies collide instead of extra ammo)