Tried it myself and it works. Only downside is you need to install their downloadclient to get it. (browserintegration not needed during install)Register at greenmangaming.com and pick a game you want.
Add it you your basket, and then apply coupon “1FREE-PROMO-WORLD” and that game will be completely free.
Highlights include:
Beat Hazard
Crash Time 3
Cryostasis
Dark Sector
Darwinia
Elven Legacy
Dawn of Magic 2
Grand Ages: Rome
Infernal
Kings Bounty: The Legend
KrissX
Men of War: Red Tide
NecroVisioN: Lost Company
Ninja Blade
Obscure 2
Painkiller [Black Edition]
The Void
Trine
Uplink
VVVVVV
World of Goo
Zombie Driver
As for the games of choice, most are rubbish but some like trine are worth playing.
