I went ahead and made two changes per your your notes. I've added ammo pickups to motivate player movement. I've also added "hard mode" (on by default) which creates the effect that overlapping potions of different colors are immediately neutralized and will not hurt enemies.
I think you're right that this gets the player moving and makes for a more exciting game. You have great design instincts!
If these notes affected your rating of the game, re-evaluation is greatly appreciated :)