It's just that the styles seem almost opposite..
The rest of the art is very outline heavy, with lots of slick details, a desaturated palette.
I'm pretty jealous of the style actually, it's something I wish I had come up with.
The characters, especially the faces look pretty standard for chibi characters and mobile/social games.
I'm not saying they look bad, far from it, but they don't stand out as much as the cards and gui.
I'm curious as to how you'll be blending the styles together.