Coming from Leica and Olympus film cameras, I'm used to 21mm lenses that are quite a bit smaller than this one. It's only small in comparison with modern bloated zooms, which I won't carry around at all. Nevertheless, it's the sharpest W/A I've ever had, especially at f4. There must be some variation in these lenses--I was a bit scared to buy it, based on these reviews, but mine is excellent. It doesn't like stopping down too far, which is common with the W/As I've had, but to make up for it, I can't get it to flare under any conditions. Even against the light, shadow detail is strong and contrasty.
My favorite lengths are 21 and 28mm, and now I have a 20 on film, and a 30 on DSLR. That's really not a bad deal, all things considered.
Too bad about all the plastic (I particularly don't like the printed rather than engraved markings and the plastic window), but I guess it's proven itself over time.