For those unaware, Mistborn is set in a world where ash falls constantly and people are utterly divided into nobility and peasants, who are little more than slaves. The ruler of this world has had the job for a thousand years (in the first book of the trilogy, at least) and is reckoned to be immortal and invincible, a god-like creature universally feared.
The game, Mistborn: Birthright, is to be set in the early years of this reign of terror and will be an action RPG. The innovative metal-based magic system will obviously feature heavily (the website, http://www.mistborngame.com/, has the line “Test Your Metal” below an allomantic table).
Perhaps the best news is that Mr. Sanderson himself will be writing the plot and most (maybe all) of the dialogue, so it’ll fit in perfectly with the world he’s created.
It’s in the early stages of development, so there’s not much more in the way of concrete info, and the approximate release date of Autumn next year could be changed, but it sounds like it could be good.