My quick review
This lens could be better for the price I paid at the time (€510). I like this lens a lot for the professional feel, colors and of cours the wide angle. Optically my copy has a flaw and unfortunately I noticed it too late.
- Good (not great) sharpness at most of the frame. My copy is decentered and doesn't give justice to it, but the sharpest side of the frame is good at f/5.6. I normally use it at f/8 or f/11 and the sharpness improves significally.
- Like my Nikkor 35mm f/1.8, this lens produces great colors and saturation. When coupled with my Hoya HD polarizer it really shines.
- Great focus speed, and it's really silent. The focus ring feels very professional as well as the full body itself, like all EX lenses.
- Excellent flare resistance, especially for a wide angle.
- No CAs at whatever aperture I use.
- Sharpness could be much better across the frame.
If you don't expect tack sharp images this lens is a must have, and a great buy considering the current street price. If sharpness is so important to you get the Tokina 11-18 f/2.8, but expect a lot of other optical problems like CAs and flare. All things considered I give it a 4 out of 5.
My copy has a very soft top right corner. Check your copy for this and get another if yours is decentered too.