For better or worse, Obama seems to have chosen to treat this event as sort of an intimate evening with Rick Warren — that just happened to be nationally televised. McCain, by contrast, treated it as a straight campaign event: he had his stump speech talking points ready, and he was eager to cram as many of them into his 50 minutes as possible.
I don't know if this was a good decision on Obama's part, but I don't have any doubt that he'll choose a much more direct speaking style at his three face-to-face debates with McCain. This is why I think comments about how Obama will need to "lift his game" this fall are off base. This wasn't a preview of his debate style, it was just a look at his style in a different setting.