Why does my iPhone game, Thick Lips, suck in United States?

I am an indie iPhone game developer living in Hong Kong. I’ve developed the game “Thick Lips“. This game got pretty cool sales figures in Taiwan/Hong Kong, but not in US. Please take a look at the game (http://thicklips.eddyl.com), and comment to advise why the game sucks (and how to make it better) in United States. Thanks for your help