In terms of the level of discussion, it was quite a good debate: to get into policy in this much detail treats voters as adults, which is a good thing.
Both had their moments. One of Obama's best moments, I thought, was his recitation of Romney's failure to be specific about his plans: on which deductions and loopholes in the tax code he would propose to close, on which parts of Dodd-Frank he would keep and not keep, on what he would replace the Affordable Care Act with. Romney's reply, that he is laying out principles and would hammer out details in consultation with Congress, didn't really cut it. Romney made an interesting statement or two about weaknesses in the Dodd-Frank rules (e.g. 'qualified mortgages' have not yet been defined) but didn't really lay out his own alternative.
That said, in terms of effectiveness of overall presentation -- not substance but style, if you will -- I think one has to give this first debate to Romney. He hammered continually on certain points -- the $90 billion Obama has devoted to green energy, the $716 billion supposedly taken from Medicare -- the latter a false charge but the figure will stay in some peoples' minds. And Obama could have replied on the first point by bringing up global warming and the vital need for alternative energy -- which he really didn't -- and he didn't specifically reply on the false Medicare charge, though he did effectively criticize Romney's voucher plan. This is one of these debates where a review of the transcript alone would probably yield a draw but on the screen (computer screen, in my case) Romney seemed, as Shields said on PBS, happier to be there. And Obama was perhaps too 'cool' where an occasional flash of real passion and old-fashioned irritation (not anger, but irritation) might actually have helped. But I don't think in the end that it will sway many votes one way or another.
Update: Award for good line to Dan Nexon: "Romney's muse is unfettered by the shackles of truth and consistency."