Substantial vignetting (in line with that of the Noctilux, qualitatively speaking) at f/1.0 and even at f/1.4, but that was to be expected. Resolution at full aperture and whereabouts is sufficient at best. This too is not surprising. Significant barrel distortion, and that was a real surprise to me. Lastly, the unfortunate habit of Canon to design heavy and bulky lenses (the Noctilux is half of the Canon 50/1.0: is this because of the AF?). Someone should explain the rationale to me, I just don't get it.
Any 1.0 lens has a ton of appeal, and indeed there are situations where the extremely shallow depth of field becomes a creative tool in the hands of the photographer. But my take is that the 50/1.0 is by now a somewhat old design and the new 50/1.2 a much, much better use of one's money. For collectors of exotic pieces of glass --- and Canon's 50/1.0 is undoubtedly a milestone in 35mm lens design --- the story is of course different.