I`m with Raze and Elliot on this one. It's more the total package, a game isnt defined only by it's cartoony or dark graphics. If I just get the feeling that the entire game fits nicely together, I'm happy. Cartoons doesnt mean that more adult themes cant be handled, just look at Pixar's Up and Wall-e.
I just wanna give the developers creative freedom, so I get surprised with the things they come up with. As long as you dont make it teal and orange like hollywood movies do too often.