In many way's it's a fantastic lens. Built like tank..very confidence inspiring. I own this lens and I'm quite happy with it...but it has one quality that is nagging me all to heck..it absolutely stinks when it comes to flares.
Compared to the Nikon 10.5 fisheye (yeah the Tokina is not a fisheye, but a rectilinear wide-angle) it is atrocious when it comes to flares. It doesn't create very nice sunstars either, whereas the Nikon 10.5mm has virtually zero flares and handle shots with the sun it, like nothing else I've ever seen.
I personally consider the Tokina an indoor/evening lens more than anything else. It's great for party shots, architecture etc. with it's comparatively sharp corners and apertures. But it doesn't do everything I hope it would and I find myself needing the Nikon 10.5mm often.