Despite the huge amount of swearing I did at this game... 5/5. Because it's simple. Because it's hard enough to be challenging but easy enough that you always get through to the next level before you want to give up in frustration. It's short enough to play in one sitting. There's no penalty for failing except the ticking numbers to make you feel bad :P. And despite shouting "I HATE YOU" at the computer screen, I still played through to the end, so I must have liked something! :) Very good game.