Probably the best lens I've ever used. And I've owned a lot across many mounts--Sony, Pentax, Canon.
Why? Because it's not just good in one area--it's excellent in almost all of them.
Wide aperture
Sharp even wide open, incredibly sharp stopped down just a bit
Smooth bokeh
Great build quality with smooth focus ring, metal feel, no rattles
Very little chromatic aberration
Little vignetting
Unnoticable distortion (unsurprising given the focal length, but still)
Compact given the aforementioned specs
Only downsides:
No weather sealing
Not f/1.2 or f/1.4... but either of those would make it much larger and much more expensive
Why? Because it's not just good in one area--it's excellent in almost all of them.
Wide aperture Sharp even wide open, incredibly sharp stopped down just a bit Smooth bokeh Great build quality with smooth focus ring, metal feel, no rattles Very little chromatic aberration Little vignetting Unnoticable distortion (unsurprising given the focal length, but still) Compact given the aforementioned specs
Only downsides:
No weather sealing Not f/1.2 or f/1.4... but either of those would make it much larger and much more expensive