Portal 2 started off as a very different game: one without Chell, GLaDOS, or even portals. Speaking at Game Developers Conference in San Francisco, Valve writers Chet Faliszek and Erik Wolpaw talked about the many concepts they had to throw away before they crafted the game that ended up being one of the best games of 2011.
For example, what's that above? It's a rare look at the game's canned competitive multiplayer mode. "While it's fun for about two seconds to drop portals under people and things like that," Wolpaw explained. "It quickly just devolves into pure chaos."
The original concept for Portal 2 featured a different main character, but the concept behind how the game would start was largely the same. Here, the player is waking up in a gorgeous environment designed to look like paradise--but it quickly falls apart in The Truman Show-fashion, revealing that the player has been trapped in a relaxation chamber for an unknown period of time.
Before deciding on reviving GLaDOS for the sequel, Valve explored setting Portal 2 in the past. It would be a prequel without portals, one where Aperture Science's Cave Johnson would be the villain. Without an ominous robotic overlord threatening your life, Valve played with a number of ideas for robotic partners--like Betty, seen above.
The co-op story was also different. Originally set after the events of Portal 2, GLaDOS originally sent the robotic pair on quests to find human "artifacts" in order to become more human. One such artifact was this comic, obviously inspired by Garfield.
Portal 2's original ending was quite the opposite of the astronomical finale gamers were ultimately presented. One concept had players needed to use a voice command to take back control from the game's final villain. Poking fun at Chell's apparent muteness, the game would fade to black as Chell uttered one word that would close the game--"yes."