I see quite a few people find their XCD 90mm disappointing, even compared to full frame zooms such as the FE 24-70 f2.8. I know not everyone's copy is disappointing. There's probably a lot of sample variation because even these people report getting much better results from a 2nd copy of the ssame lenses.
But what I want to know is: for the copies of the 90mm that are disappointing, what eactor is bad about it? Sharpness? Vignetting? CA? Others?
I already know a somewhat common complaint is the hexagonal bokeh
i think you are referring to my experience with the 90....
i got to try the X1D with the 45 and 90 and must had been handed a bad copy that day....since these were demo items i thought it was strange that nobody else seemed to have noticed....the 90 looked pretty bad compared to the sony GM zoom and the 45 looked a lot better or at least what one would expect from a system like that....
i really wanted to walk away from that day with files that would give me what i had been missing shooting with FF dslrs and mirrorless, but i did not....the 90 looked worse, the 45 slightly better but i knew that the camera (which was at that point an early release firmware) just wasn't going to work for me.....as great as it looked and felt in my hand, i just could not see how i would be able to depend on it for people work....
i was able to try the camera and 90 combo again later, when the firmware was updated and included the moveable AF points.....that copy of the 90 was much better but the implementation of the movable AF points....not sure why they bothered....
either way, i don't think there is anything "wrong" with the 90....i am sure it easy to return and exchange if one gets a bad copy....the bokeh issue obviously won't go away, but that is a known thing at this point and seems to be a choice for the entire system....