One very good thing, as you mentioned, is that for an F2P to succeed - it REALLY has to shine.
A game can be free all it wants, if I'm not enjoying it, I'm sure as hell not going to dump ANY money or additional time into it.
It could bring about a massive revolution in the quality of games in the market, if it becomes mainstream.
Game companies would actually HAVE TO compete for our time/money/attention by the QUALITY of the game, and not the hype.