I let a friend borrow my Fuji X100s over the weekend for a concert he was shooting and in return, he lent me his Olympus Zuiko 55mm, f/1.2. I've never used a lens with such a large aperture and it really is just a completely different experience.
The backgrounds are incredibly textured and swirly which can give a nice emphasis to foreground elements. I think you'd need to be really careful that the background doesn't distract from the intended subject though.
As you can learn quite easily from a quick google search (and these photos), this lens is fairly soft at the maximum f/1.2 aperture, but there is a dream-like effect you receive in exchange. If you are looking for a sharper image it's just one click over to f/2.
The glass in this lens is enormous which you can see in my selfie here or John Carey's desktop featuring another copy of the same lens.
Overall, this is a really unique piece of gear. Like pretty much any lens with a big aperture, it does stuff that your standard lens can't pull off. I'm not sure I need one, but it sure is fun!