Valve has announced a new promotion going on right now in anticipation of the release of Portal 2 for Steam users. Right now buy and play anyone of the games offered in their Potato Sack. What’s the Potato Sack, you may be asking yourself? The Potato Sack is where 13 of the best and hottest indie games are on sale. From the super hard surprise hit Super Meat Boy to the dark horror of Amnesia. Buy the games and play them. As you play the corresponding meter on http://www.aperturescience.com/glados@home/ will fill up. Fill up all the meters and GLaDOS will unlock Portal 2 for PC and MAC Steam users.
There are two things really cool about this promotion. One its encouraging gamers to play some great offbeat indie games at a really affordable price and two by buying these games they are helping the indie developers make a bit of profit to make more cool games, all the while unlocking Portal 2. So if you like offbeat games and plan to play Portal 2 on PC or MAC buy these games and play them. The sooner the meters fill up the sooner Portal 2 will be available on Steam
Source: Portal 2 Blog