Here's a really interesting op-ed posted on Agency Spy today. The comments are shit, so don't bother reading them, but the post is really interesting.
The guy who wrote it was involved with the recent Kenny Powers MFCEO work and seems to know his stuff (he worked at W+K before moving to Sunny). He's touching on the importance of The Big Idea but in a slightly different way. He thinks, rightly so, that great ads should be able to be stretched out into a great film.
Of course this isn't always the case—it might get a little boring to watch 90 minutes of The Man Your Man Could Smell Like or Most Interesting Man In The World, although those are great ads. But it's a pretty big indication of whether or not your campaign has "legs."
So go read "Nice ad, but would it make a great movie" and start thinking of your own ideas.