Well what else can I add that has not already been written? Of course this might be the sharpest non-L lens that you might add to your collection. Even sharper to my eyes than the EF 85mm f/1.8 that I sold to fund this macro lens.
I own a D60. This camera is known to hunt for an accurate focus in low light. A few reviewers reported hunting with this lens, whatever their camera is. I found it to very extremely fast and dead on, even on my "old" D60.
Build quality? Feels like it can last ages even under the roughest handling.
This lens is not underated, every photographer seems to know what it's worth. Nor is it overrated. I could not try it before I actually purchased one. I only heard about it and read reviews but I can tell you I was really short of breath when I looked at the first pictures taken.
This is an amazing piece of glass. Period.