I think the best comment I can make about this great little lens is that I have been using it for a couple of years now and it has begun to replace my 24-70/f2.8 AF-S zoom as the lens which lives on my FX Nikon for most of the time.
With the tiny 35mm/f2 on my Nikon, I regularly end up with better pictures than when I strap on the mighty 24-70mm/f2.8. Obviously the 24-70 allows you to zoom between a good range of focal lengths but I have found that in most situations, you can move your shooting position to compensate for this. I guess that for some subjects this is not possible, making the zoom essential.
Protrait photographs are the obvious area where one wants to stay slightly further away and use the perspective of a 70mm+ lens for best effect. In this case I would suggest a 35mm/f2 and an 85mm/f1.8 or secondhand f1.4 as a better combo than a trditional 24-70mm mid-zoom. In addition, I have found it possible to take some really nice portrait shots with the 35mm - generally full-length shots; with the f2 aperture isolating the subject nicely even at this wide-angle focal length.
It's also worth bearing in mind that the 24-70/f2.8 costs nearly FOUR TIMES as much and is a stop slower than the 35mm f2!
Optical quality of the 35mm f2 is superb, giving bright contrasty images across the whole FX frame. As mentioned above, the f2 aperture is very useable indeed. I have taken several shots where the images from the 35mm f2 are noticeably sharper than any zoom lens such as the 24-70mm.
Although an AF-D design, AF speed is extremely quick, due to the simple construction and tiny size of the lens - it's hardly ever noticeably out-paced by modern AF-S designs.
At this price tag, there are no real down sides to this lens and, as several reviewers have confirmed, it can represent something of a do-it-all lens for many photographers. If you regularly need to go very wide, zoom in way past 70mm or photograph where your viewpoint cannot change, then you may make the call differently...