This is a 30+ year old lens, so most of the negatives would be common for all of the lenses from that era. And to get the negatives out of the way: it's large, heavy (for a mirrorless user, anyway), unstabilized, with a screwdrive motor that is somewhat noisy and not fast (not slow either, though). Some CA, some loss of contrast in some lighting situations (again, typical for a lens released in 1985, and easy to fix in post.) It's sharp, but not super sharp. Out of all these cons, the only two that really impact how I use the lens are weight / size and the lack of stabilization.
Now the pros. The lens is known for it's beautiful creamy bokeh, and wonderful colors, which were the two primary reasons I bought it. It did not disappoint. I use this lens for portraits, and it's been good enough that I didn't buy a 85mm prime. Also, constant f4 is a plus.
I would not recommend the Beercan as a general purpose tele, unless you have a body with IBIS and don't mind carrying a DSLR size lens around. But as a portrait lens, it shines.