This game requires a free Steam account to play.
Use voucher code FIFTY-SAINT-XMASS to get 50% off of our price listed! You can pick up the game for just $19.99 / £13.29 / €17.49! Voucher expires: 1000 GMT 26th December 2011. (9PM 26 Dec. AEDT)
Cheaper than most Russian keys, so this is an absolute bargain IMO.
If you're feeling generous, then you can use my referral link which credits both our accounts with $2.00: http://www.greenmangaming.com/?gmgr=fununuga
Great price for a great co-op game