Well, as you probably already know, there's a demo of Kingdom Hearts. I say give it a try. I downloaded it but as soon as I found out that the CPP support wasn't available in the demo, I turned it off. Never liked the Kingdom Hearts series but there are plenty of people that absolutely love it.
Kid Icarus is a great game if you can get past the inexplicably insane control setup. Even now, I still am not comfortable with any of the interface options.
I think you're going to be satisfied and disappointed (at the same time!) regardless of which one you choose.