s1e5697291wrote a review of Shimano Ultegra RD-R8000 Rear Derailleur on May 5, 2018
Familiarity: I've put it through the wringer
Purchased this to replace my Ultegra 6800 short/med (honestly, not sure which it was) cage to ensure compatibility with an Ultegra 11/32 cassettte. All I know is that according to Shimano, the R8000 Long Cage is required with a 50/34 up front and 11/32 in the rear.
o So smooth that shifts are often completely transparent, i.e., "did I actually just switch gears?"
o The B adjustment screw actually does something.
CONS (not really CONS, just notes of caution):
o The B adjustment screw actually does something. ;-) This adjustment now definitely affects indexing and you need to pay attention to getting it right. See any number of YouTube vids on the subject.
o As I suspect is the case with any long cage derailleur, hanger alignment is critical. My short cage shifted just fine with what turned out to be a pretty badly bent hanger. The R8000 would have none of that, and simply refused to shift well even after hours of performing all the standard adjustments. If you can normally adjust a rear derailleur in 15 minutes, and your new R8000 has taken 3 hours with no luv, your hanger is bent. You can probably get it very close with a tape measure and spare wheel screwed into the hanger, but the Park tool or the HAG from Abbey are the official tools of choice, or your LBS.
o The geometry of the cable pull is completely new/different. You might need to adjust the length of the chain stay cable housing (I had to shorten mine). Also, the R8000 is pretty intolerant of excess cable dangling past the lock screw. The excess needs to be trimmed pretty short (~30mm) and/or bent to ensure it doesn't interfere with the derailleur or spokes. I left mine long while performing inital adjustments and it got caught in the spokes about a dozen times before I temporariy zip tied it off in an un-offending position.
In short, as is typical with Shimano, their high end tech is trickling down to the mid and lower ranges and defintely does not disappoint.