This isn't really a job offer.. But I'm genuinely curious why not just pay someone whose work you already like instead of setting it up as a contest?
Seems like a very round-about way of getting nowhere, especially with even just seeing the brief being behind an account sign-up page. I can't imagine anyone actually doing all that work for the 'chance' of maybe getting paid (it includes sprites, so basically all assets I guess).
If you want options, studios often require small art tests, but they are rarely more than a couple hours work, not the entire game, and normally you'd only invite them to do that if you were already interested in working with them, minimising wasted time - much more respectful!