My initial gut response was a bit flat. Reading the speech later it certainly reads a lot better than it was delivered. But then there may be a few reasons for that. I think it didn't make good use of his natural speaking style and flow. At times he seemed to be getting into a stride and then he had to change direction and tone suddenly.
Also I wonder if the sheer size of the crowd and bank of cameras in front of him was a little off putting. It certainly seems to have gotten to the chief justice and he only had to say 35 words. That might also have thrown Obama a little as his great moment of triumph (the swearing in) was not picture perfect for the ages. As a result the correct swearing in had to happen in a small room a day later with no crowd or TV coverage. If I was in his position I would have been hopping mad deep down inside. Lucky for the Chief Justice there aren't any more possible promotions.
Finally I think the message and tone of the speech was one of hard work to come. A speech in the style of his victory speech may not have conveyed the idea that he is now getting down to work. On balance it sent out the message he wanted and hasn't dominated the news cycle since allowing space for coverage of his first actions rather than first speech.
Did it set a benchmark in the public mind that all debaters will be judged against? Well hopefully it will remind people that both matter and manner are critical to a successful speech and shifting the emphasis from one to the other can be key to setting the tone and message.