All you have to do is like THQ’s official Facebook page and receive the steam code. Metro (THQ)’s official page stated:
“For everyone asking where to retrieve their free Metro 2033 PC download key, please visit the application at FreeMetroGame.com or click on the “FREE Download” tab from our page”
What are you waiting for? Go and download it! I already have a copy of Metro 2033, so if you don’t want to register a Facebook account, let me know below and you can have my Steam code.