I have to say I was more interested in this before I saw there was a prescribed art style.
Constraints are both useful and necessary in the creation of art. I imagine that they may run future competitions with different style guides. IMO I think it's brilliant. A variety of artwork submitted by a variety of artists with the expectation that they'll all potentially be useful together. It's pretty ambitious and a style guide is totally necessary.
My only complaint is how do we ensure the appropriate quantity of animations for character assets? The diversity of assets will determine how much freedom coders have to present gameplay principles. It may not cause problems though- it just depends.