I haven't seen any reviews for this lens anywhere. I was very interested in getting an ultra wide angle and/or fisheye for my 40D. However, being that it is a crop camera, we all know the difficulties with that . I have the Canon 10-22 and am very happy with it, I just wanted wider. The canon 15mm fisheye was my next choice, but it is not much wider than 10-22 on a crop, I have also heard that it has problems with CA and is soft at the corners. I then became interested in the sigma. I have not owned any third party lenses. I don't really buy lenses to save money. I buy lenses for their ability and image quality. That being said, I have only owned Canon and half of which are L. I was very interested in the sigma for the fact that it is designed for a crop, and offers almost 180 coverage, but a little hesitant due to the fact that it was third party Let me just say that I am so far impressed. IQ is excellent, it is usefully sharp wide open and excellent at f/4-5.6. It does have the characteristic "sigma" warm color cast that I've heard about. However, it's not terrible, it's just there if you know what you're looking for. It can be easily corrected if you shoot RAW. It focuses fast, accurate, and silent. Also, build quality of this lens is excellent, comparable to "L". It has some weight to it but, it's not too heavy. Overall, EXCELLENT lens! if you're looking for a fisheye for your crop this is a very good choice.
. I have the Canon 10-22 and am very happy with it, I just wanted wider. The canon 15mm fisheye was my next choice, but it is not much wider than 10-22 on a crop, I have also heard that it has problems with CA and is soft at the corners. I then became interested in the sigma. I have not owned any third party lenses. I don't really buy lenses to save money. I buy lenses for their ability and image quality. That being said, I have only owned Canon and half of which are L. I was very interested in the sigma for the fact that it is designed for a crop, and offers almost 180 coverage, but a little hesitant due to the fact that it was third party 
Let me just say that I am so far impressed. IQ is excellent, it is usefully sharp wide open and excellent at f/4-5.6. It does have the characteristic "sigma" warm color cast that I've heard about. However, it's not terrible, it's just there if you know what you're looking for. It can be easily corrected if you shoot RAW. It focuses fast, accurate, and silent. Also, build quality of this lens is excellent, comparable to "L". It has some weight to it but, it's not too heavy. Overall, EXCELLENT lens! if you're looking for a fisheye for your crop this is a very good choice.