This is pretty insane... there's also a daily drawing to win 5 games from your wishlist. Steam is the greatest.
Edit:(might as well add some more info to this post)
Seems you can do the previous quests to qualify for the grand prize, which removes some of the pressure to try and get those 10 objectives.
Forcen has posted all the specifics 2 posts down. (insert arrow pointing down)
It is also important to note that you do not have to buy every game. If you already own them you get the ticket for the drawing assuming you get the achievement or whatever.