Well, it has taken a while to get around to it, but I have finally replaced the Sigma 10-20mm lens that I had back in august.

I was eager to really try and test this lens out and compare it to the sigma. Is the canon at almost twice the price, better than the sigma? Well, if you want to look for yourself, then here are the test shots.
I have tried to replicate some of the test shots I did to the sigma so you can compare them between the two lens.

Pro's.

-Very precise and good feel manual focus ring - Constant manual focus and non extending barrel.
-Excellent results with the test shots overall.
-Overall zoom range. Of the "ultra" wide lens currently on the market, the Canon has the best range.

Con's.

-Typical Canon build quality and reminds myself of my 24-85mm F3.5-4.5 lens. Unacceptable at this price point.
-Price. Every way I look at this lens, it is over priced. It cost more than my 70-200 F4L, wieghs half as much and is certainly not built like an "L".
-No included lens hood or lens case. Compared to the other three ultra wide lens currently on the market, this makes the higher price even harder to justify. 70-200mm F4L included lens hood & case and cost less.
-Lens hood. It's big at 110mm in diameter making it very hard to fit into a typical gear pack. It is far larger than the sigma's lens hood. Having to pay for it as well left a bitter taste in the mouth.

Summary.

Overall, an impressive lens. It is pretty clear so far going by these shots that the Canon is better than the sigma. At the price of the canon it had better be.
After comparing the canon to the sigma I was left wonder what the comparision would have been like if I had a good copy of the sigma. It's pretty clear that the two copies of the sigma had centering issues and victims of Sigma's hit & miss quality control. if you can get a good copy of the sigma could well be the better lens. But for me, I ended up with a great lens. Ok, it cost a lot more. But after a while I forgot all about the price. Good & clean photo's tend to do that.