For a well known political figure Hillary Clinton has managed to maintain a remarkably strong public image over the past few years. According to Gallup, 59 percent view her favorably while only 37 percent view her unfavorably. Those are extremely enviable numbers. From Gallup:

Trend: Favorability Ratings of Hillary Clinton

You are looking at a big reason why so few Democrats have expressed interest in entering the 2016 presidential primary. Clinton has complete name recognition, a massive war chest, and broad popularity.

If she runs in 2016 her image will be damaged some. That is what campaigns do. You can see how the 2008 campaign brought her down by several points, but her personal image is now notably stronger than it was at this point in the last election cycle when she was only barely leading in the primary.