What to say? Well... maybe the best way to express it by offering up the words of some others.
From http://www.time.com/, there's Joe Klein telling us that "Obama's Victory Ushers in a New America" or Nancy Gibbs giving us "The Meaning of Obama's Win: How He Rewrote the Book".
Really, though, the best words to use are from the man himself...
Other YouTube videos from Obama can be found at http://www.youtube.com/user/BarackObamadotcom.