It's a grossly underestimated lens with very nice bokeh, that's where it will differ from the Nokton. I read somewhere that the rendition is very similar to that of the late pre-asph Summicron 35/2 but I haven't had a chance to compare them yet (I just got a 35mm and will develop the first roll on Sunday). Once the weather improves from wet snowfall and winds approaching storm speed, I will make a comparison between my 35, 40 and 50mm.
You might have seen that people have modified their 40mm to bring up the 35mm framelines instead of the standard 50mm frames. To me, the inside of the 35mm frames of my M6TTL is a perfect match on distances above 2-3m. Older M's (M2/4) have slightly bigger framelines that matches the 35mm better.
If you want some images from the 40mm, check out my pictures from the RFF Euromeet in Paris (link in my signature), most of those are taken with my 40mm.