Gamersgate is already doing something like this...
http://nvnews.net/vbulletin/showthread.php?t=182222
Basically you watch 2 commercials and play an entire game for free... how is that a bad thing exactly? Heck even if they put a commercial between the games chapters (Dark Void is the game I download and its told through chapters) this could be a great benefit to gamers to provide us cheaper or free games (as long as they don't use this in $60 retail games).