As you can see from the sample images, the lens is rather soft wide open. In my view, this is no disadvantage and I would not like the lens to be sharper, since the overall- look of the image is more harmonic like that when shot wide open. The transition from in- focus- areas to out- of- focus- areas is very pleasing.
On the second photo you can see that the bokeh balls are rendered egg shaped, but the overall quality of the bokeh is smooth and non- distracting.
The colors which are coming from this lens are saturated and punchy, which befits well the way this lens renders in general. The way this lens renders tonality, which is best seen in black and white is it's biggest weakness in my opinion. You can get punchy black and white photos, but I wished the gradual transition of values would be a little better.
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; I would not give it away anymore.