This review documents my experiences on a dx camera; your results will likely vary for full-frame usage.
I purchased this lens since I quite like the 40mm focal length for general-purpose photography (ok, 42mm on dx if we want to be pedantic). After over a month of dedicated usage on a d7000, I will say that this can be a tricky lens to use.
It's fairly sharp wide open, though I've found f/2-2.8 to be my minimum for acceptable sharpness. By f/4 and above it's as good as you'd ever wish a wide-angle nikkor prime to be. Nonetheless, as much as I wanted to deny its existence, focus shift does occur around f/4-f/5.6 with a tendency to back focus. You can control it by being mindful of your settings and shooting in aperture-priority, but I definitely had a far lower in-focus keeper rate compared with the 35mm dx or the 50/85 f/1.8gs I also shoot with under the same conditions.
However, while the 35mm dx is generally sharper, the 28mm's flare resistance and bokeh are noticeably superior.
Build quality is plastic. Fine for my purposes, but take care not to bump into anything.
With all this said, I'm keeping the lens, as its results are truly stellar. Just be mindful that there may be a bit of a learning curve with the lens. (As an added note, my copy required a -10 fine tune adjustment.)