Portal 2 writers Eric Wolpaw and Chet Faliszek revealed in a talk at GDC that the beloved sequel was almost a very different game. When they first started writing scenarios for it, they considered removing Chell, GlaDOS, and, of all things, portals themselves. They would have replaced GlaDOS with a different version of Cave Johnson, Aperture's founder, as well as a knee-high bot named Betty.
Portals would have been replaced with something called "f-stop," nomenclature that makes sense given that a camera's "aperture"—how wide the lens opens when it takes a photo—is often referred to as its f-stop. No idea what that would have translated to gameplay-wise, though.
In any case, when Valve presented the new mechanics, story, setting and characters (including a blonde, non-Chell player character) to play testers, fans were apparently "disgusted and insulted." So they put those familiar elements back in and crafted the wonderful tale we now fondly know as Portal 2 around them.
We can't help but wonder if there will ever be a Portal 3, and if fans will finally consider the original's material exhausted enough to allow the writers free reign to create a new scenario. We're sure this bizarro version would have been great, if not exactly the Portal 2 we wanted.
Are you glad they stuck with Chell, GlaDOS and portals for Portal 2? Would you want another Portal game to explore more unfamiliar territory? Let us know in the comments or on Twitter.