Well - it is without peers,,, It has a very long working distance and amazing Bokeh due to the large blur-circles, it's not f1.6 up close I think it's f/2.2 or something but you really don't find any other 'macro' lenses with those specifications,,,
Some of the Exotic Micro and Macro Nikkors come close in performance but they cost between 2-200 times the price or even more,,,