The general premise is that you can accomplish two or three things in a presidency. Kennedy didn't do much other than the Cuba standoff, but you can argue that he was successful purely because he motivated an entire generation of progressives. Reagan accomplished quite a bit, including the end of the Cold War and the end of the welfare state and the era of big government, which were his aims.
Clinton didn't do much of anything. No education reform, a lot of cowardice and inaction in the face of international crises, no gay rights reform, no national health care. He got NAFTA through, but it wasn't his baby. The economic boom increasingly appears to have been largely artificial, and real income per worker has continued its generation-long decline.
I suspect Clinton will be largely seen as having squandered a huge opportunity for change. The popular will was there...he simply failed at Washington politics. Now, the GOP deserves equal blame there, but you have to judge someone on their achievements...I don't see many for Clinton.