She's Al Gore Part II if she runs. We're (and by this I mean Democrats) just going to give it to her. I do think she'll be an effective leader. We might be years removed from her crusade for healthcare reform as First Lady, but I feel she's still progressive at heart.
The President is only as liberal/conservative as the Congress that sends her the legislation. Hillary would bring a strongly Democratic wave with her into Washington.
If you're progressive, you'd be better off with Hillary than a "true believer" who spends their entire term arguing with a Republican Congress.