I think many of the commentators tonight are focusing on the individual exchanges and missing a big picture win for Obama tonight.
In many ways McCain, like it or not, is nearly an incumbent candidate, almost like running as a sitting VP.  He is tied, fairly and inextricably, to almost every major policy implemented by Bush.  Even his more mavericky positions against the tax cuts and torture have been watered down to "I agree with the President."
People don't want another four years and, despite his use of the word "change,"  that's very nearly McCain's pitch.  Tonight, McCain, faced with an actual opponent, couldn't bring himself to parrot the pretty, bipartisan, I'm-the-changiest BS that he delivers on the stump.  He brought the full range of conservative positions and Obama, for the most part, brought liberal or moderate positions.
So there were no big tactical wins, no major gaffes, and very little memorable.  But on the optics, the 50,000-foot view, Obama nailed it.  He stood at that podium, took questions calmly but decisively, contesting every lie and distortion from McCain, interrupting when necessary.  He looked like a real President.  And for the middle slice of the electorate who don't agree with McCain on policy and can't stand Bush, trust in Obama is the last bridge to cross.
Obama doesn't have to beat McCain with witticisms and superior rhetoric.  That's nice for us chattering elitists, but it won't win over the undecided middle.  What will win them over is the big-picture messages.  Obama projected confidence, wisdom, determination, and a tiny dose of righteous anger in unpacking McCain's distortions.
Americans want to vote for someone new, but they're afraid and need a gut-level reassurance that this guy is real and up to the task.  Seeing the two men on the same stage as equals, by itself, starts to break down the myths of the war hero and the empty suit.  McCain, in reality, today, is not so heroic, and Obama is not so empty.  As the voters' idea of these two men approaches reality, Obama will benefit and McCain will lose.