I've heard good things, played with it for about 20 minutes on a D800 while I was in Portland.
Initially, it looks good. I couldn't tell if there's any complexity to the distortion, but it looks like it distorts less than the Tokina. Edge sharpness was pretty good for being that wide, and resolution was pretty awesome as far as I can tell from the back of the screen.
You should play with one in a camera store, if you can find one that carries it / you'll be in the area. Besides that, get onto a site that allows for some pixel peeping.
I only got this impression from the little shooting I was able to do in the store, but I'm a little worried about the contrast / color rendition. Obviously I would have to mess with it, but it might have just been crappy lighting that's more apparent in an image, as I'm completely satisfied with the color rendition of the 11-16.