This looks pretty good...
You'll play as that apprentice and go on missions for Lord Vader, but your existence must be kept a secret, so this will give you an opportunity to battle rebels, Jedis, and any unlucky Imperials who happen to get a glimpse of you. The developers consulted heavily with George Lucas on the story and characters, to the point that what happens in The Force Unleashed is now considered Star Wars canon.
Star Wars: The Force Unleashed Updated Impressions - Gameplay, Graphics, Story - Wii News at GameSpot