I think your definition of "underage" is basically wrong. What you mean is light-hearted or just simple-minded or whatever. Let's take for example Nintendo games. They are not meant to be for children. They are meant to be for everyone. You don't have to make a deep, grim or complex game to offer entertainment for all kinds of people and ages. D:OS is definitely not writte especially for teens or kids, not at all. But of course it's not as "deep" as old Infinity Engine games. But let's be honest: few people would read that much again while playing games anymore. Playing BG2 is like reading a book and playing a game at the same time. Great experience at its time and an all time classic, but not every game has to be like that.
I agree on the cliché issue. But then again D:OS is playing with clichés and often there is a humorous twist to them.
