Is there some back-story to this game that is interesting? Are these spheres of mutant gel being produced by the evil Dr. Klaus Scheitzenburger to turn children into mindless drones so that he can take over the planet and only I can stop it using my Mutant-b-Gone sphere blaster?
Oh, none of that? It's just a sphere popping game? There's no marketing that can save that.
Now a killer back-story isn't a requirement, but it would help if it were "juicy fun". There's some great advice here: http://www.gamasutra.com/view/feature/2438/how_to_prototype_...