He could/should have been waaaaaay better, but I won't blame him for appearing frustrated and pissed off with Romney, considering that all Romney did was lie, lie and lie.
Even if Romney did lie, Obama, since he would know that they were lies, should not have been bothered, really. I may be a naive optimist, but if you know you know the truth, you shouldn't be ticked off by lies about you.
The truth is, Obama was in full form last night, as far as his personality is concerned. He is really a man-child, with a very thin skin. Last night, he demonstrated that by acting peeved and snarky, which is unpresidential by anyone's standards.
The truth is, Obama blew it. If Obama was proud of what he accomplished the past four years, he would have acted like it. He would have been able to field off Romney's attacks with the uttermost confidence of the success of his record. Instead, he came of as an amatuer, at times seeming to look to Lehrer for help. He couldn't even bring himself to look at the camera for more than 5 seconds, much less stave off Romney.