My first reaction is that the speech was extremely smart and intellectually subtle. It's very unusual for a politician to give a speech that works at such a high intellectual level. At every turn he resisted simplifications and added nuance.
This in turn reminds me of one of the things I like about Obama's candidacy. He may be liberated to operate at a high intellectual level in public because he's black. I'm not trying to be Gerry Ferraro here; let me explain. Candidates like John Kerry and (even moreso) Al Gore were also very smart, but constantly forced to dumb it down lest they be tagged as out-of-touch elitists. Since the egghead image is so at odds with the prevailing stereotypes about African-Americans, he has much less to fear by speaking at a high intellectual level.
Of course, Obama is extremely intelligent -- as smart as, or smarter than, any presidential candidate I can ever remember. Yet I don't think a brilliant white Constitutional law professor could pull it off. Being black obviously disadvantages Obama in all sorts of ways. But this is one way where it helps.