I'll start by saying that the 85mm 1.8 USM is not a  bad lens by any means. In fact, I feel that it's one of canon's best values. Mine was sharp wide open, focus is fast and accurate most of the time, and the bokeh quality was excellent. For most people there's no reason to look for a 'better' 85mm lens. The only drawback was that shooting wide open, or near it, in high contrast situations, resulted in some crazy purple color fringing. You can usually fix that in post with one click though, so it didn't bother me. And to be completely fair, all other 85mm primes suffer from the same issue- the 85L is no exception. 

 

If you really love the 85mm focal length, don't mind carrying around a MASSIVE/heavy lens, and can cope with super slow autofocus, the 85mm 1.2 might be for you. It costs five times what the 85mm 1.8 does though - a price that's hard to justify. I use 35mm 1.4 and 85mm lenses most of the wedding day so I decided to give the L a try, and I got it for a very, very fair used price. 

 

So was it worth it? For me, yes. I love this lens, in fact, it may be my favorite lens of all time. Wide open at f1.2, it's razor sharp. The colors are much more saturated than the 85mm 1.8, and the contrast is significantly better. If you are shooting tons of images with a particular lens, these things save you a lot of time in post processing. F1.2 is a full stop faster than f1.8, and this opens up new possibilities when shooting in low light situations with no flash. It's the difference between using ISO WTF, and a reasonbly high ISO. It's the difference between being able to get a motion freezing shutter speed or not. It also obliterates ugly backgrounds in a way that f1.8 does not. On the other hand, the AF is super slow (because it has to be so precise) though very accurate, you have to have the camera on for the manual focus to work (it's connected to a motor), and it's heavy. Very heavy. Other gripes: the rear element is flush with the lens mount, making me scared every time I mount or dismount it. The lens hood attaches to the focus ring and spins, which is annoying- and if you put your camera on a surface, it rests agains the lens hood, which puts pressure on the focus ring, which may cause it to wobble over time/loosen up. If you are shooting sports, this lens is not for you. If you are shooting portraits, stills, weddings, etc. you will absolutely love it if you can afford it.