And it's 1kg and 15cm long, and costs 1300 too. Most people will probably rather buy the non-art 28 and a 45 and carry both. But I think that's besides the point. If you're buying this I think it's because you really want exactly these bells and whistles.
The art line is like the "enterprise edition" of lenses :-)
Once I get a really good lens of a particular type I find it hard to use a similar lens that is not so good. I cannot get over the quality of photos with this lens
I like it even better than the much more expensive 135mm G Master I have except the autofocus of the 90mm is too slow to shoot volleyball indoors.
Sometimes I think I'd like to try a lightweight lens and/or a lens with a very wide zoom range, but in the end I can have convenience and come back with photos that aren't so good and a lot of times you get just one chance to take a shot so why take one that's less than it could be?
Unless you like the constraint of not being able to zoom. There's something to be said for having to move within a space physically in order to compose a shot.