It's difficult to convey a lot of "meat" in a 30-second, expensive TV ad, so Obama's campaign may have had to choose, because of limited finances, between image advertising and "meaty" policy advertising. I doubt that Obama can convince the general public to vote for him based just on policy positions; he has to first convince voters that he offers a more attractive alternative to Hillary, and that will be difficult enough. After all, Hillary has been in the public eye for quite a while, and whoever even heard of Obama before his election to the Senate in 2004. Voters who are undecided about Obama may have to seek out his positions via the internet rather than wait for ads that spell them out. His website (here) contains a great many detailed expositions of his policy positions. I think his campaign has done a great job in a short time, considering his status as a relative newcomer to presidential politics. Hillary has been gearing up for this for quite a while.