Plenty sharp for current 21/24MP cameras. Very good contrast and color. Better in that respect than any Canon L primes I have owned and comparable to Zeiss Z* 21 and 100mm lenses. This lens has very good separation of photographed subjects from each other and from the background (which I believe some people call "3D effect"). This lens has very good flare control. I haven't seen any veiling flare so far and if you shoot directly to the sun, the reflections are minimal or none.
The only negative comment I have about optical quality of this lens is tendency to show purple fringing. I saw it mostly in initial testing in harsh light at f/2, but I have it in some real life pictures as well. Most raw converters will remove it automatically, if you turn this feature on.
The lens has minimal focusing distance of 24cm/10", which gives interesting creative possibilities. The lens has floating design and retains good sharpness at both ends of the focusing scale.
The build quality seems excellent and focusing is very smooth. I think the anodized finish is less forgiving than rubber and polycarbonate of professional lenses from Nikon and Canon and will scratch easily. The time will tell.