If it doesn't come up type Metro 2033 free on your facebook box. All you have to do is Like it.
This is an amazing marketing move to hype up people for the next launch title. I know Bethesda has done this and released Vaperware Elder Scrolls titles which is really cool since Activision and other companies that have bought out older studios make it hard for anyone to sell old copies of popular titles but you guys go above and beyond. Any change you might release a free game of a recent title?
EDIT: Btw the product code you get is for Steam so you'll keep this baby for life!