decent...
there's been times when I kept forgetting which button is for up or down. And even then, I"m not even sure if whether i went up or down a level. If only there is a way I can tell for sure. One great way is to gradually shift the color of the walls to another color depending on how high or low you go. For a ridiculous challenge to your hardcore fans, start using keys and locked doors, teleport, traps, and all sorts other things.