As you can see from the sample images, the lens is rather soft wide open. In my view, this is no disadvantage since the overall- look of the image is more balanced like that; the character of the photo becomes painterly, feminine dreamy. Like this, the transition from in- focus- areas to out- of- focus- areas is very harmonic.
On the second photo you can see that the bokeh balls are rendered egg shell shaped, even at the center of the image at open apperture . Yet, the overall quality of the bokeh is very pleasing.
The colors which are coming from this lens are saturated and punchy, which befits well the way this lens renders in general. The rendering of tonality, which is best seen in black and white is weak, when compared to other expensive lenses. You can get punchy black and white photos, but hey lack in microcontrast and richness in tonality.
Chromatic aberration can cause some problems, as you might expect from such a fast lens. Just be aware of it.
The construction of every lens is a trade- off. Since the Nocturnus is built for extreme speed, there are some downsides by definition. I actually do love this lens and it gave me fantastic images; even though, this lens has some weaknesses as well. Some of my most beloved images have been taken with this lens actually. It is fun to use and it gives you enormous artificial possibilities. I would never give this lens away anymore.