I'll give it a shot...
Obama is incredibly articulate, and can make a very convincing argument for his agenda. He sounds calm, and confident, his posture and demeanor represent the USA well in foreign policy and negotiations. He's fairly consistent with his positions, and at this point, you know what you're getting if you put him back in office. He's willing to back policy he believe in (healthcare reform) even when it's not politically beneficial to do so. For that reason i believe it's fair to say he operates in a more principled way than most politicians do, whether you believe in those principles or not.
Romney refuses to speak to issues where his party's position is unpopular with the nation. While all politicians attempt to direct attention to the issues where their views most align with the voters, Romney does this to such an extreme it's unusually transparent and makes him look weak and fake. Romney's position on healthcare reform is extremely weak. There are very few voters who don't want Obamacare, but would welcome a similar system in their state. Romney's greatest asset ought to be his business acumen yet, in a federal government that spends over half the money it collects on entitlements, one wonders if Romney will be willing to make the tough, unpopular choices necessary to affect any real change.
*I'm cheating as I'm not sure I've entirely convinced myself to vote for Romney yet. I'm very disappointed in the republican offering this year.