Nice, considered review Ramon. I have the 85 f/1.2 II and had the 135 f/1.2 at the same time for a couple of years. My impression of the two was that the 85 had a little more "magic' that is hard to define, but that the 135 had a kind of relentless sharpness that was quite good for its speed and focal length.
As to build, my 85 came flawless out of the box and I haven't noticed anything negative - no mechanical weakness, unintentional disassembly or dust problems. As to focusing, yes, it's slow, but, as others have mentioned, the focus motor has to move a group of very heavy lens elements. In any case, hardly anyone seriously buys this lens for fast-moving low light sports (a few diehards to the contrary). Its best use is for slow considered portraiture and even some specially rendered product shots and other miscellany, all done in a style where ultimate focus speed is almost irelevant.
I find its bokeh to be impeccable, but I hardly ever shoot this lens tight at f1.2 (maybe for an occasional half- or full-body shot), due to its insanely narrow depth of focus; if your subject so much as twitches, your f/1.2 shot will be a mess of misplaced focus. I find that f/1.6 is a great aperture for my purposes with f/2.0 being not much less attractive. At f/2.8, you might as well be using less expensive glass, although this lens is still quite amazing through f/4.0, compared to most others. It's not just sharpness, it 's also the "character" of the image: a combination of designed-in flaws and aberrations from the purposeful trade-off demanded by such a wide maximum aperture, its bokeh, its color, its contrast and the super-high center resolution along with dimiinshed edge and corner results. This is supposed to be, above all else, a portrait lens, and all these characteristics make it a great one. For instance, when taking a good head and shoulders picture, it is the central area of the subjects face, around the eyes, that benefits from great sharpness, not the tips of the subjects' shoulders on the edge of the picture.
When I have to quickly shoot a lot of portraits of a lot of people, as in a day of corporate "gang" shooting on location at some headquarters conference room, I always use my brilliant 70-200 f/2.8 IS II. It get's the job done perfectly, and you can somewhat make up for f/2.8 bokeh by using a longer focal length when possible. But for those occasions when I can take my time to get a really impressive single "portrait" picture, I like to use the 85, and slowly vary the focus to see what I can make of the very narrow band of focus that it affords me. For this, there is absolutely no substitute.
All in all, a terrific lens I will keep indefinitely.