I couldn't be happier with this lens. I like this lens so much that this is actually the only time I have wanted to post a review. Perhaps I just got lucky with a "good" copy, but regardless this lens is wonderful.
I made an even trade for the lens with my 17-40L, so I was a little concerned if I had made a mistake. But after two days of shooting with it, I couldn't be more pleased.
Shooting on a 1dMKII, there is virtually no barrel distortion, the lens is sharp throughtout the range and frame, the CA is virtually non-exsitent. I really love doing landscape work, and I already can't imagine how I lived so long without it.
It was tuff giving up the "L" glass, but I'd do it again in a flash. The Sigma now perfectly compliments my 24-70L, 70-200ISL, and 100-400L.