As you're not looking for any sugar coating, after watching the video showing the gameplay you would need to pay me to want to play it. The reason is that there is no "why" to it. Shooting low-resolution textured balls wasn't fun in the late 80's, and I'm not seeing anything in the video that tells me it won't just be a chore to play.
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.
I'm not sure 'purpose' is the right word here. Truly what is the purpose of a game? I don't think there's a trivial answer to the question, and I think 'story' is more fair. People care about stories. Stories generate meaning.
I can't speak for anyone else but for me purpose, if I distill the meaning, means that I walk away from the game richer.
Eg
I have experienced an interesting emotion due to a story and the characters. Or I have realized a principle thanks to an interesting strategy (happened to me lately with Defense Grid - I realized I shouldn't build the longest path possible but maximize the times an enemy walks around a defense tower; this translates directly into books I'm reading now about featuritis and user experience - minimize the number of features, maximize their usefulness).
I'm not a native speaker so maybe there's a better word for it that eludes me.
Edit: Story is definitely one (maybe the most important) cornerstone of purpose!
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_...