I have had one for a few days now. For me, the jury is out. It doesn't seem to provide high-contrast or "pop" in the colors when wide-open, like say, a Zeiss. But that's OK with me (much easier to add contrast than remove it). I just processed some Thanksgiving pix with the M8 and Nokton, and I had to bump the contrast on pretty much all of them (but not the saturation).
I'm still struggling with focus issues at larger apertures. Mine seems to back-focus a bit wide-open (as opposed to my Sonnar, which does not), so I'm learning to adjust for that.
I need to get out for an M2-day with it and see how I like its signature on film.
To be brutally honest, my little VC 35/1.4 SC is looking pretty great right now at 1/2 stop slower, cheaper, and much tinier.
If it helps, I've attached one of the better results (at least it's in focus, not calling it a great photo) from Thanksgiving. The first has a few minor adjustments (exposure, rotation, sharpen), but no contrast or saturation adjustment. The second has contrast and vignetting added to the first (again, no saturation). The lens has a UV filter on it, but is not coded.