Thank you guys, really really awesome feedback here!
@sunandshadow: Great list of taboos! Some may be a bit out of the scope of the project, but others are spot on. In fact, I have to thank you for broadening the idea of taboos, I had only thought of them as conversational taboos, as in things you can't really talk about (such as sex in a really conservative Whisperer village). Your ideas really expand on that, and I particularly like stuff like the seasonal one (the game will involve deity festivities and events that might impose temporary taboos like that).
@Orymus: I certainly want to convey the image that Shining People are thoughtful, but it wasn't my intention to show them emotionless. In fact, the Whisperers would be closer to the Vulcan idea of emotions than them. I picture the Shining People like less evil Dark Elves from R.A. Salvatore novels, intellectual but also very prone to passion and emotion (often negative). In contrast, the Whisperers behave more like Japanese society; polite, reserved and calm.
You're right that in case of The Shining People it may be hard to put together these two concepts. I think it works best if you picture them in a frame of moral ambiguity (not sure if I'm making sense there) they're highly ambitious, and often see themselves above good and evil, so if killing an "inferior" foreigner is needed to protect their people, they will not hesitate to do it.