Well, in my mind, there's a way to execute the cutesy/appeal-to-younger-audience style in a way that doesn't turn off other age groups... ironically, it was Nintendo who did it the best I can think of, and that was, again ironically, Pikmin, the game from which LKS draws so much inspiration. The art direction in Pikmin was nothing short of brilliant. Yes, the name was strange, the characters were cute, and the juxtaposition of "realistic" environments with these cartoony character designs was questionable, but... it all just works so, so well. Other examples: Alien Hominid/Castle Crashers do the cute/cartoony look well, and of course Wind Waker and its cell shading was awesome too.
I've played quite a bit of this game now, and the gameplay has me addicted. It's just excellent, and is really hitting my "Pikmin craving" I've had for awhile. Don't get me wrong, the game definitely has some serious style and polish, and I've been able to overlook my issues with the presentation... I just disagree with the decision to needlessly take it in a "kiddeh" direction.
P.S. – That "the story makes it make sense" shouldn't really need to come into it, as that's cart-before-the-horse territory. But noname2200, I'm honestly pretty curious to figure out what that means now.
