I agree with Paul Richardson that a discussion of what makes a software product compelling and enticing for its intended audience would be helpful to us. Quite often we happily go about designing and developing software that captures nobody's heart other than our own.
I do not own an iPhone and I am probably too old to use that particular software even if I did carry an iPhone or there exists ports for my mobile phone. However, just by looking at that lone pic you pasted sends me laughing. For such a subject matter, I thought the art and theme of the app was absolute class. And I suspect that has something to do with the number of people who install that.
I am also supposing the majority of such users are going to be of a younger age group, so 99 cents is not likely to eat too much into lunch money and requiring fasting for three days. Heck, for 99 cents most folks may even play with it for a week to a month, then uninstall it forever. I know I spent alot more on lotteries, and I am not even habitual at that. If you can position your twinkle app at a "disposable" or "throw away" price, buyers are less likely to regret it even when it is not a great product.
My nomination: Bejeweled