I think there may be some slight variation in the first batch, based on my experience, which isn't conclusive - (could be a one off).
First lens I received #(000061) was soft at 70mm f/2.8, had a hazy appearance on focus area. even once calibrated with lens align2 I wasn't blown away
(I had the Tamron 24-70 vc and returned it because of back focusing and poor AF quality & speed).
Even though I wasn't wowed by the first copy it, it was better than the tamron, in every way. I still returned the canon the following day, considering the price, I wanted AMAZING.
I was lucky that my store had a second copy of the lens yet to be sold (000063) which they kindly exchanged.
Now I am super impressed, amazingly SHARP @ F2.8 at every zoom length across the entire frame, which is inline with what Roger at Lens rentals reports. no micro adjustment required. (after doing the usual lens align procedure).
DID all sorts of exhaustive tests, and real life shots, I am wrapped with the build quality, operation, and images which come from the lens....I don't know if there is slight variation between copies, but this is my experience (first copy compared to second) and could reflect the photo zone findings.
The onion bokeh is there under certain circumstances, but its allot cleaner than that of the Tamrons, and isn't noticeable unless pixel peeping. doesn't concern me in the slightest. I think the bokeh is wonderful, very similar characteristics to the 50L1.2.
lack of fringing and CA is great. colour and contrast is wonderful.