Removing four lines at once with an I-piece in Tetris is the most efficient way to score, which creates a tension: on one hand, you want to build high enough to score quickly, but on the other, building too high puts you at risk of ending the game. The balance between the two is exquisite.
I mention that, because I was about to grumble that the corresponding balance in MEI Maths’s new game app thingummy Factris isn’t quite as good – of course it isn’t. Nothing ever will be.