One of the things that I love about this lens is the focal length. I've tried photography at 35mm and always found it too wide and 50mm too confining at times. The 45mm fills that gap completely. It gives a wide angle feel of the 35mm but the framing of the 50mm. Another thing is the size. The lens looks absolutely miniscule compared to the D800 and I can not emphasize how light my camera is now. Did I mention how creamy the bokeh is?
While I love the focal length and the size of the 45mm, it does have its drawbacks. There is a minimum focusing distance of 80cm which restricts on how close I can get to the subject. Another thing is that when focusing close up, the focusing is quite finicky and requires a lot of concentration even with a focusing screen installed. Last but not least, sharpness. The photos produced at f/2.8 tends to be a bit fuzzy, but it starts getting sharp at f/4. Although I mostly photograph at f/4 and smaller, it would be nice to get slightly crisper photos at f/2.8 in lower light situations.
Even with its drawbacks, I still have to say the Nippon Kogaku GN Auto Nikkor 45mm f/2.8 is one of my favourite all around photography lenses. The focal length makes it easier for me to get the shots that I want and the size is a plus. While the focusing does take a while to get used to ( it also turns the "wrong" way), it is a fun nifty lens that I'd recommend having if you can find one at a decent price.
More sample images here