That game looks pretty neat. You just sold a copy :) But it's a game I've never heard of before, and I'm pretty good about checking the new games lists on the App Store each week. So I think the takeaway from this shouldn't be that premium games (is $2.99 really "premium"?) don't work, but rather that you can't rely on free marketing to sell your game. Once a game falls off the lists, it's pretty hard for people to stumble across it unless they're looking for it specifically.