I don't use facebook, but this may be of interest to others.
Saw this on Eurogamer….
THQ is giving away the PC version of moody first-person shooter Metro 2033 for free.
All you have to do is like the Metro Facebook page. Once done, reveal the Steam code, load up the app and download the free copy of the game for Windows PC. The offer runs to 16th December 2012.
Good find.. I already have it but I'll let some friends know.