Quite impressive a lens (and pricey too...). Let us start with the worst aperture, f/3.5. Vignetting is apparent. Distortion is low. Contrast is not bad. As for resolution...
Well, the far left side looks soft, but... if you push the sharpening, this is what you get:
There is a lot of detail there. "Soft" and "mushy" are two different things. Of course, f/3.5 is not the ideal setting. Here is f/8 :
Not bad, really - I could have pushed the sharpening here too. But better correct CA. With CA corrected, this is how the foliage looks like (upper edge) :
... not very sharp, but the focus was more distant, so this is normal. Now, without CA correction :
And I prefer not to show the corners. But, as CA correction is simple and automatic, why bother. Another nice thing with this lens is its relatively low distortion. See for instance the following example :
Close-ups work OK too :
Conclusion: a good performer (and an impressive piece of optics, about 600g and quite compact...). But, the price being the same as for a new 14-24 G, the latter is a better buy for all practical purposes.