I've done 3 pro shoots with the R6 and 1.5.0 and have delivered some worse pics to clients due to problems so i've just reinstalled 1.3.1 as that worked better before in these same areas
Main issue to me is a large group shot night event high iso, exposure simulation looked fine, resulting file was 1 or 2 stops brightly overexposed. I found out a bit late as i don't want to chimp continuously while working. The next group shot had the same issues but i was aware by that point so i did some test shots before to bring down the brightness difference of exp sim to file so they got the right exposure. I don't want to have to do that every time and never needed to on 1.3.1, i could trust the viewfinder sim exposure
Next as mentioned by another, back focused near ears instead of eyes like some past mirrored dslr issue. A simple action set of a kid coming down a slide, all on ears, before on 1.3.1 fine on eyes after a few similar shoots
The only thing i wanted improvement with 1.5.0 was for it to better know which is the closest eye, 1.3.1 chooses distant eye often and 1.5.0 just as bad so have to manually override often to get closest eye on shallow d.o.f portraits/candids. Also better understanding a face is a face when just tilted a little away from frontal would be nice
And we shouldn't need eos utility to downgrade firmware if we have it on a memory card ugh, should be allowed internally
Anyway, after that glass of whine relieved to have 1.3.1 again