I think you need the perspective of history to judge the Greatness of a President, and that perspective does not exist yet for Clinton. My inclination is that he will be middle of the road and not a candidate for Mt. Rushmore.
On the other hand a failure does not need the historical perspective, it is evident pretty much immediately. Dubya and the Cheney admin was a failure in my view as an abject liberal, and since they laid the ground for a huge opposition victory in terms of the executive and legislative branches must be so viewed by the conservatives.