You can hardly find any real 2D games in the shelves anymore, except for entire collections of retro games as one product. Todays top notch "2D" games are pseudo 2D, the images are textures on some quad meshes facing the camera. This allows for many fx that are hard to achieve in real 2D, like antialiasing, blendmodes (esp. addition for sfx) rotate, scale, sub-pixel-placement, zoom, alpha, light, shadows, particle, fog, fragment shaders.... Therefor, 2D is fine when you use the latest technology, that is in effect 3D, resembling 2D. Real 2D, like we had 100 years ago, meant: masked sprites only, not even an alpha channel. You won't earn much respect when you challenge todays 2D games with original, real 2D. But the concept of 2D games, like sidescrollers, point'n'click, hexa tiles, topdown etc. is still well perceived, if the graphics are up to date and real eye candy. Above all that you need a theme that has an audience.