I'd try to make your two major elements bigger: the logo and the girl on the unicorn. I admittedly don't know KQ, but I feel as though the mountain behind her likely isn't as important, and yet takes up almost half of your composition's center. I'd zoom in on the girl, maybe even letting the unicorn horn break the plane of the circle, letting us see the background elements over her shoulders instead of above her (and I'd desaturate the colors in the castle to match the mountain).
In addition, I would spread the KQ logo until the red ribbon was almost touching the outer edges of your picture.
You may be correct that this image is too busy. You could get rid of some elements, but I think you could also work with the saturation of colors so that all of the secondary images aren't competing for our attention.
All in all, though, I like what you're doing with this art, and the game. I will probably be inspired to make your game my first sojourn into the world of KQ.