I would probably put in more game modes or enemy types. Maybe a maze to navigate or have random points to hold like a king of the hill mode. I can see this game appealing to a family with 2-4 kids and having the parents throw them the iPad while camping/waiting in line. Sustainability in this type of game is hard since it needs more content and variety. I found the challenges get old pretty quickly. You could also probably make money by selling different weapon pickups or backgrounds.
IthrynLuin
joined
Have been playing games for decades and modding for almost as long. Recently hooked up with some friends to bring back local multiplayer games. Proficient at concept drawing, in game art, 3d modelling, texturing, rendering and animation.