Read this Pew analysis, which works through the exit polls in some interesting ways. A couple of highlights: the "God gap" didn’t really narrow all that much (indeed, in one way of looking at it, it widened); and young (18-29) voters went very strongly for Democratic candidates. Note also that Catholics were the swingers, though those who attend weekly still narrowly supported Republican candidates.
A question about this to which I don’t have the answer: were Democrats more effective than Republicans at revving up young supporters, or has the character of youthful political allegiance really changed that much?
If this doesn’t satisfy your political jones, Jay Cost offers one of his wonderfully wonkish analyses at RCP.