Personally, I view The side-scrolling space shooter genre as a niche market. People who enjoy and seek out S^4 games are looking for either a 'bullet hell' game like Ikaruga(1) or a nostalgic game like R-type(2). Side-scrollers are great game design practice, but the market is full of very discerning customers that would much rather pay 5$ for an emulator than buy an unpolished, depth-less, programming experiment.

I do not say this to bash the game. I have a list of android apps I hope to program, and a side-scroller is halfway down that list. At the top of that list is a tip calculator. It would be foolish to charge 10 cents for a tip calculator. I would be even more foolish to draw broad conclusions from the very small number of sales. But the most foolish thing I could do is call it quits before I get to the apps in my list that don't exist in the market in a dozen variations.

(1) http://youtu.be/EGNSdcy-apU?t=2m30s

(2) https://play.google.com/store/apps/details?id=com.dotemu.rty...