Yup it's a superb lens, definately one of the best of the super wide bunch. Not only does it have excellent IQ but it's built to last and outshines both the Sigma and Canon versions by a long shot. Consider the 11-16 if you plan to do a lot of low light shooting or or you really need that extra mm.
EDIT: Don't have any experience with Nikon WA lenses, however there are a couple I know that are apparently as good or better. Also I've never had any problems with CA on my lens, which I did find odd as it's "well known" on the lens. It's very rare that I get any, and in fact it out preformed most of my old lenses in that respect (canon Kit lens, Sigma 24-70. 75-300 IS), although my 300 f/4 used to be better at handling...