pretty cool.
but personally, i don't like games that are totally based on gameplay where its hard to play without totally focusing, and if you do totally focus, its way too easy. so its basically just based on how much the player is concentrating, and nothing else.
i do like it, but i think you could add something that makes it less annoying in that sense. for instance, you could make it so the numbers move, or the numbers change sometimes.
anyway, good game .