Valve's Chet Faliszek and Eric Wolpaw conducted a Portal 2 postmortem at GDC last night. The writers talked candidly about alternate endings and the difficulties of following up on their critically acclaimed first game. Chet also mentioned that, at some point in development, the team experimented with competitive Portal 2 multiplayer modes.
Chet also mentioned that they sucked. "We also tried a competitive multiplayer mode which we put together over the space of a month or two," he revealed. "It was a mix of the old Amiga game Speedball and Portal, except with none of the good parts of either of those two. The game was super chaotic and no fun, so the only good news about this part was that we cut it pretty quickly."
Speedball 2 was a competitive, violent, and featured an incredible soundtrack, and I love the Aperture Science Handheld Portal Device as much as the next man. That said, I can imagine this combo resulting in a confusing mess of nonsense. Valve made attempts to satisfy more competitive gamers by including leaderboards and a challenge mode in some later DLC .