Fun little game. I can see a lot of cool ways you could go with this, and give it more challenge. Maybe the waiting period between the green guy's charges could get shorter as the game goes on, Maybe have the enemy's direction be based on a prediction on where the player will be, or as Roark said, put a countdown on invisibility.

Cool game but there is a bit of lack in the goal. If you had add maybe a score that would go up and maybe a count down on the invisible because it is overpowered but other than that it is pretty cool