Summary: This lens was designed to be used on a crop sensor camera, but I chose to use it on my full frame camera. I'm a big fan of vignetting, so at 10mm, I get the vignetting on the sides. At 13mm there's still a little vignetting at the corners, and then none as you increase the focal length. Of course on a crop sensor camera, vignetting is not a concern. And because it is not an EF-S lens, I am able to use it on both my full frame and crop sensor cameras if I want.
Summary: The zoom range on this is just right for my needs. I shoot a lot in narrow streets in Mazatlan, MX and had a hard time "fitting it all in" before I bought this lens. I mostly shoot at 10mm but the "zoom" to 24mm eliminates changing lenses in many instances. This is my third Tamron lens and I find them all exceptional and don't see how anything could be much better unless it would be an L lens... which I will never have>.
Summary: I've had this lens for about 3 years now, normally using it for my normal lens on a Pentax digital camera. One can always quibble about resolution, but the final question is, "what do the pictures look like?" The answer to that is that the vast majority of photographers will see little difference between this lens and your others, regardless of price. When I first got into photography in the 60's, I, as well as most of my peers, felt that we needed telephoto lenses.