More than an actual harmony on each department, it's FANTASTIC. I'm in love of each element this game offers.
Though I gotta say I didn't realize until level 19 that cannons do have an anticipation animation when shooting. Maybe it's a bit too subtle.
But for almost everything else there's a great enough amount of contrast. There's a perfect amount of both style and clarity.
In the end I would buy this game. You deserve that!
PS: There's a bug of freezing the screen black when opening the menu during a transition.