At first glance the focal range for this new Tokina lens doesn't look that impressive at just 14-20mm. That's barely more than a 1.4x zoom range, so it's enough to help you fine tune the picture's framing without having to change your position, but hardly a zoom lens at all in the accepted sense.
It's barely even a super-wideangle lens. That 14mm setting is equivalent to a 21mm lens on a full frame camera, so it's a lot wider than a regular kit lens but not as wide as other superwideangles, such as the Tamron and Nikon 10-24mm lenses (15-36mm equivalent).
But one thing sets this Tokina lens apart from all the rest – its f/2 maximum aperture. First of all, it's constant across the whole zoom range (such as it is). The key fact is, though, that it's a whole f-stop faster than even the best of its rivals.
Well, almost. Let's not forget the Sigma 18-35mm f/1.8, a pretty amazing constant aperture zoom in itself. But while the Sigma lens is a fraction faster (only one-third of an f-stop, though) and has a better 2x zoom range, it's a longer focal length lens, equivalent to 27-53mm in full frame terms. So it's more of an ultra-fast standard zoom, while the Tokina is an ultra-fast extra-wide zoom.
Like the Sigma, the Tokina 14-20mm f/2 is designed for APS-C DSLRs, not full frame. It comes in Canon and Nikon mounts. There's no news yet on availability or pricing.