I have created a simple game that you can download, play with and submit to the store – both to Windows Store and Windows Phone Store – reching millions of users world wide. It contains the basic functionality of a 2d sidescrolling shooter game.
This game starts simple, then after level 3 – more enemies will come, and after level 4 there is a possibility that a harder enemy that takes two shots to kill will spawn.
The game supports input of touch, mouse, keyboard and the xbox controller just connect it to a surce or a computer and play!.
This game is pretty simple, but with your modifications to it, it can be a totally new game with much more content.