I put a post up on my crappy game-design blog about VVVVVV's successful exploration of a single mechanic. It's basic, and probably has a few holes, but those curious can check it out:
http://game-0.blogspot.com/2010/02/flipping-out-or-one-mechanic-is-all-you.html (http://game-0.blogspot.com/2010/02/flipping-out-or-one-mechanic-is-all-you.html)