As for the substance, I thought he did a pretty good job making his case why the McCain policy agenda is too much of the same and bad, and why his (and the Democratic agenda) is good, and the change we need. Naturally, a lot of this depends on whether one agrees with the policies (and even I had issues with some his proposals), but he's speaking to a Democratic audience. Sure a lot of it was traditional Democratic fare, but it's a Democratic year, after all.
One of the prevailing memes from many on the right is that it was an angry speech, and not very inspiring. I think it was appropriate to attack McCain on policy, but pro-McCain forces contend that he attacked McCain personally, and accuse Obama of attacking McCain's courage and patriotism. I didn't see that at all, but this is the offending phrase:
"You know, John McCain likes to say that he'll follow bin Laden to the gates of Hell. But he won't even follow him to the cave where he lives."
FWIW, I don't think he should've used that line, but what I think Obama was doing was advancing the argument that the Iraq war was a distraction from the hunt for Bin Laden. It's a sloppy argument, and not one I agree with, but Obama was hitting at McCain's policy judgment. The thing is, the line is problematic for three other reasons, the first being that it ignores the reality of the Bin Laden situation, the second being that McCain has no authority as Senator to catch Bin Laden (nor does Obama), and third, it contradicts Obama's own wise point about impugning the motives of those with whom we disagree. McCain and Obama disagree on the best way to fight the GWOT, but it's bad form to even appear to imply that McCain doesn't want to go after Bin Laden. That's just as bad as suggesting that Obama puts his self-interest ahead of the country, or that he'd "rather lose a war, than lose an election."
I suspect Obama felt the need to play tit-for -tat, but it does hurt the speech somewhat.
I thought he closed out well with his change and post-partisan theme, although he still has the problem of lacking a real legislative record to back that up.
Oh, and then there's Sarah Palin, who was a surprising and impressive choice by McCain. The Obama camp may not have gone too negative last night, but their dismissive and almost haughty response to Palin is disappointing, and may only serve to drive away more Hillary voters. Is he really going to try to use the inexperience tag? Not good at all on that score.