The first M-Mount lens I ever bought was the Voigtlander 40mm f1.4 Nokton, and I was amazed by its small size and metal construction. The aperture ring was in the "wrong" place and it had these lovely little focusing and aperture changing aids on its incredibly small barrel. I bought it to use on m4/3 as a fast medium telephoto lens. I then used it on my M8 and sold it after buying my M9 when it became frustrating to use because of a framelines problem.
My idea behind buying this 35mm f1.4 Nokton Classic was to pair it with the Voigtlander 75mm f1.8 as a two lens kit. This would give me two fast lenses, should I need that, with two focal lengths that I like and suit the Leica. If I'm happy with the 35mm I intend to work with just these two lenses on the M9.
My initial tests with it wide open didn't go well. I tried it in a fairly dark environment & was missing the focus. At f1.4 on a full-frame camera you have to be pretty accurate with this. I eventually got used to it and here are two examples.
In common with many fast lenses its not at its sharpest wide open and like Voigtlanders I've used doesn't have great bokeh. But its very acceptable. Stopping it down it gets sharper and sharper, f5.6 - f16 are superb. I need to use it more to come to a final conclusion but initial impressions are good.
I used it briefly on my GH1 and again it seemed very good, very similar in performance to the 40mm.