I love mine, it's essentially glued to my 6D.
It does have some quirks though.
Its motor is noisy, kind of squeals when it's running, you can even feel the steps it takes while focusing as a subtle vibration in the camera body.
Many lenses, you can grab the manual focus ring at any time and take over, not on this one, unless you take auto focus away from the shutter button, as in back button focusing, probably other combinations too.
If you do set to back button focusing and set the lens switch to MF, you do get focus confirmation while BBF is held, I like how that works.
Manual focus also goes to sleep after 20 seconds or so of inactivity, a tap of the shutter button wakes it back up.
I also considered the Voitlander 40mm Pancake which got some rave reviews, others not so rave. Turns out the Voitlander is more susceptible to flare, has a bit of barrel distortion and a fairly repulsive onion skin bokeh, never mind no auto focus at all.
Bokeh on the Canon is smooth, somewhat oval shaped, under normal conditions, just about flare proof though I did get some extreme flare from streetlights above and just behind me to the sides during night shooting recently.
With the 6D's high ISO performance, the Canon's f2.8 maximum is a non-issue speed wise, no worries about dealing with razor thin DOF either.
Auto focus speed seems fine to me, but I've little experience with high line lenses to compare.