Ah, who doesn't love a good nuemonic? Here is a great one for making a serious adventure.
F: Freak. A freak is a great way to make a symbol, or put in a bad guy. (Zombies work well)
A: Action. A good battle is always neccacary, even if it is symbolic. (Good vs. Evil)
I: Intrest. The Story has to be good, or nobody will care about your game, or your message.
L: Lesson. Every serious adventure needs a moral to go with the story.
Hope this helps somebody the next time they make a serious adventure!