A good solid lens that does its job well, if not spectacularly. I bought this lens to replace my copy of the f/4 version for cubic panorama shooting, and I'm very glad I did.
The image circle will have a bluish border to it, but unlike the f/4 version of the lens, vignetting has been eliminated, and the CA is much better controlled. And while a shade sharper than the f/4 version, it's still difficult to get tack sharp with the lens. Live-view has gotten some pano shooters realizing that the focus scale is inaccurate. Focus to infinity actually happens about halfway between the 0.5m and 1m marks.
I use the lens on a Canon XT, and on a crop body, it becomes halfway between a circular and a diagonal. This is actually very useful. I merely need to crop (or in moments of insanity use a 1.4x tc) to fill the corners, and I get a much wider FoV for pano shooting. You can indeed cover an entire spherical view handheld with four shots. If, however, you plan on shooting panos with a tripod and panohead more often than handheld, a Nikkor 10.5 might be a sharper choice.