I've had this lens for just over a month, also on a 6D, and I've found that it gets me exactly the shots I want from it, provided I focus it manually. I found it a little bit frustrating the first week I had it, because the 6D's AF points are not precise enough to get high keeper rates at f/1.2, which is of course where I want to use it much of the time. The center AF point is better than the rest, but even in an ideal test setup with tripod and B&W checkerboard MFA target, I found that the 6D+85L combination would focus in front of and behind the target. It front and back focuses equally often and by the same amount, such that MFA wouldn't help (MFA is an offset, so it can only correct lack of accuracy and not this lack of precision). Also, I found that this is only true for close subjects like my test target at 5 to 10 feet; AF consistently front-focuses by a large amount with very distant subjects, those that are hundreds rather than tens of feet away. Using live view autofocus has none of these problems, but this is rarely practical when I'm shooting outdoors. It's slow, and the screen is difficult to see in bright sunlight.
So, I use this lens as a manual focus lens, with very few exceptions. I found that I had to install the Eg-S focus screen to make this workable, the 6D's factory screen (Eg-A II) just showed everything being too much in focus for me to clearly see where the critical focus areas were.
I don't consider this a general purpose lens. I would not personally choose it for moving subjects. I'll be using it mostly for portraiture and landscape, where I have time to focus carefully and get things right. If I need a similar focal length but require fast, accurate AF, I'm going to use my 100L, this lens gets a high keeper rate in seemingly every situation, without any of the effort I have to put in with the 85L.