The main difficulty for me was the speed at which some of the cookies fall combined with how big the screen is and how many cookies there are to keep an eye on. It's hard to react to an evil cookie suddenly coming at you at light speed when you have so much else to keep your eye on. I would also recommend reducing the hitbox of the evil cookies and increasing it for the good cookies, it's always a good idea to cheat a bit in favor of the player.