After the debate ended, Republicans were calling it a draw and Democrats were calling it a strong win for Biden. That tells you all you need to know.
Yet I don't think any of those things compare to this: Biden made the whole Democratic argument -- on policy and values and he hit Romney really everywhere Democrats wanted him to. He left nothing unsaid. You can agree with those points or not. But this was exceedingly important for recovering the damage from last week's debate when many Obama supporters simply felt that Obama wasn't willing or able or something to make the case Democrats around the country are hyped up to make. Why didn't you say this? Why'd you let him get away with that?
Biden said it all. And for Democrats around the country that was extremely important.
For reasons that are complicated and juvenile, during his vice presidency a caricature has emerged of Biden as some sort of Crazy Irish Uncle, gaffetastic and corny, a risible figure. That left people unprepared for what they saw tonight. Ryan was unprepared too. Biden's actually one of sharpest guys in Washington and has been for decades.
I suspect Ryan's equivocations and unwillingness to give details will be the day 2 and weekend stories. But the most critical point in terms of the trajectory of the debate was that Biden left it all on the field.