I am having a great time with this lens. I recently shot a theme event called "Going Down the Rabbit Hole" and this lens was perfect. I got some incredible captures of all my costumed friends and would have them look up into the lens and shoot with their nose only a few inches away. Very trippy & fun. It is tricky using a flash because if its mounted on the camera, it may get into the shot and directional flash will not cover enough area but I did manage to get a couple shots bouncing it off the walls & ceiling. I move a lot to get the distance and more dramatic effect as even 1 foot difference is a big difference. I think Ernst Haas said something about "the most important lens is your legs" and this lens brings that quote to a whole new level.
I haven't had nearly the CA & lens flare I thought I would so I am impressed. The build quality is very good (I use mostly L glass) and I had heard about focusing issues but my lens has been auto-focusing pretty well although I would expect a bit of focusing issues with a 180 view. With the DOF f/8 + & lens set to infinity, it has produced very nice images. I have only had the lens for a month so I am still learning to think like the lens see's but it is a fun learning curve. $899 is a bit much but I am not regretting my decision.
Love in Light, Carlton