Greg Saunders at This Modern World:
For starters, Clinton's biggest selling point has been her "experience", but as Timothy Noah wrote at Slate, Hillary's claim of experience is incredibly dishonest :
[D]uring her husband's two terms in office, Hillary Clinton did not hold a security clearance, did not attend meetings of the National Security Council, and was not given a copy of the president's daily intelligence briefing. During trips to Bosnia and Kosovo, she "acted as a spokeswoman for American interests rather than as a negotiator." On military affairs, most of her experience derives not from her White House years but from serving on the Senate armed services committee.
Even if she was able to claim Bill's experience as her own, what is there to brag about? NAFTA? Welfare reform? Don't Ask, Don't Tell? The Communications Decency Act? Easing media ownership laws? Defense of Marriage Act? If she wants to run on her husband's record, then it's worth pointing out that the Clinton Administration wasn't the progressive paradise that she's promising.
During the Clinton years, there was one big "accomplishment" that she can claim... her failure to enact universal healthcare. Considering that one of her biggest promises on the stump has been universal healthcare, I'd expect the "most experienced" candidate to have a better pitch in this regard than "second time’s the charm". If Hillary can learn from the mistakes she made in 1994, who's to say the other candidates can't also learn those lessons?
Of course, another point against Hillary is that I don't think she's truly taken the lessons of the Clinton years to heart. She came into Washington in 1992 and the GOP establishment destroyed her and her husband. She was seen as arrogant for trying to use her position as first lady to strive for universal healthcare, demonized as a corrupt witch for Whitewater, and had to sit idly by while the GOP leadership in Washington dragged the nation through impeachment. Yet though all of that, she and Bill are still naive enough to believe that they can triangulate their way towards legislative victories and trust people who have shown them nothing but contempt.
Yet once Hillary became a Senator, for all of her talk about the "vast right-wing conspiracy", she was foolish enough to give the benefit of the doubt to people who have proved themselves to be untrustworthy. She voted for the Iraq war, the bankruptcy bill, declaring Iran's Revolutionary Guard a Terrorist organization, etc. She's obviously not as bad as the Republicans in this regard, but for somebody who's been through the bullshit she's been through, I'd expect a little more skepticism.
Check out the rest for an assessment of the other Democratic candidates.