If you need the link go to www.freemetrogame.com you should be redirected to a facebook page.

Thanks OP I really wanted this one.
Promotion is legit and I can confirm the key works in steam.
After you get the key it tells you to download an installer but you can skip that step and just activate it in steam instead.

I'm surprised they are giving the game away since its in the THQ' humble bundle (not free, but close)