Don't make the mistake of deciding the game is "good enough". If you're not selling 20 copies a week, the game isn't "good enough". And you CAN sell 20 copies a week. But you need to add more stuff to the game.
This is the gospel truth. I made that mistake with my first release of Bubble Bomb. After that first release I went back and refined the graphics, added extra gameplay elements (like the "bubble bonus") and a few other things. The game was WAY better in the second release because all I did was sit and think about how to improve and tweak it after it was finished. That extra polish times goes a LONG way.
Bubble Bomb will never sell 20 copies a week, but it's selling a lot better than it was during the first release.