I really appreciate this piece of artwork, and I'll tell you why. It looks like a game that was designed to make its graphics pop as though any screenshot you take could be a painting, and in the process of getting to this point, it *doesn't* go overboard. An example of a non-indie game that achieved this is Rayman Legends.
What do I mean by "overboard"? It's that in so many 2D indie games that intend to be beautiful and bright, somebody decides that the palette should be saturated with primarily ultra-bright colours and that lighting/glow effects should be everywhere. This is why I hope to see a new game that looks like the Magic Forest mockup some day. Everything in Magic Forest is balanced, and the attempt to go high-spec succeeds. It ultimately creates a beautiful-looking picture with visual clarity. Overall it's a very appealing image with good colour theory and good lighting.