If you want to know how good a lens is, look at the graphs - what is the resolving power of the lens? Knwing a true Nikon macro it will be absolutely as good as it can get...but probably only around f8 onwards. There has to be some compromise in lens design - macro lenses will be biased towards being stopped down, not wide open.
I have a 55 f2.8 micro - it si oneof the sharpest lenses ever made, by anyone. Every lens maker comes out with a real beaut every now and then. The micro Nikkors are amongst them.