I am looking to develop a game in either Unity 4 or XNA Game Studio, and I think I have thought of a rather good idea.
Basically, you can switch lights on and off, and as we all know, moths like light. There are some moths in the play space - you have to guide them over a certain area by flicking lights on and off. If there is one moth and a light is turned on, the moth will fly straight to it. If there are several moths, the moth that is either furthest away from or closest to the light (you will be able to flick between these two options) will fly to it. It will be level-based, and have a kind of grey-scale theme to it.
tl;dr version: You make moths try and get to an objective by turning lights on and off.
I doubt that this would see much success outside of the mobile market. So, develop it for Android, iOS or both, if you're feeling like making it successful. It might include learning either Java or Objective C though, although I don't know as I don't do mobile development.