If you haven't watched the finale yet, spoilers ahead:
Bart is dead. Nobody cares. His death is a monumentally insane plot device to get Chuck and Blair married so that she wouldn't have to testify against him. Although Chuck didn't actually kill his father.
Turns out that as pretty much everybody expected Dan was "Gossip Girl." The flashback explanation was good, but I'm betting if we go back and watch the series from the beginning we'll find inconsistencies in that story.
William dumped Ivy and got back together with Lily. Kind of gross, but they deserve each other.
When we flash forward five years what we'll call "The O.C." Maneuver" we see Chuck, Blair and their son; we see William and Lily together; we see Rupert with Lisa Loeb (which was REALLY weird); and we see, as expected, Dan and Serena getting married.
Happy ending. Good enough.
The highlights of the show was a brief scene in which Rachel Bilson (of "The O.C.") and Kristin Bell (who did the Gossip Girl voiceovers for all 121 episodes) as themselves got the text blast revealing Dan's identity as Gossip Girl. It's was wacky and sort of wonderful.
It was better than the show itself.