Summary: So far it seems to work fine. I haven't used it extensively. Sometimes I wish I had spent the extra money and got the Nikon lens. My Tamron wide angle lens is wonderful. I should use this Macro more to get use to it.
Summary: I read reviews by Ken Rockwell, The Wirecutter, and DP before buying this lens. It's a solid entry level wide-angle, in fact, it's my only second lens to a 35 prime. While most reviews complain it's a bit soft overall or fuzzy around the edges, I'm very happy with it. After using it for several weeks, I can see how a slightly faster lens or something with a bit of a wider aperture might be nice, but I couldn't justify the cost.
Summary: Great lens for the price. I like ultra wide but the Canon is too expensive. This does the same thing but the edges blur away rapidly in comparison to the genuine Canon. Using a small aperture helps and is good enough for the price.
Summary: This is a wider angle zoom lens than I am used to and I'm still learning how to use it. It is a well made, substantial lens. So far I've used it only for real estate photography. Unless you watch what your doing, it is easy to take photos that appear unnatural and distorted. Walk closer to the subject and the lens' wide angle of view are best utilized. I think this is a keeper.
Summary: I'm on my second one. The image quality is good for the price and it does have the better zoom range than the canon made equivalent but the first one broke because my friend somehow damaged the autofocus motor. With the autofocus switch "on" it turns the motor like on all non USM (ultrasonic motor) lenses, he turned it and turned it too quickly and hit the stop at the range of focusing. The momentum of the motor was enough to strip the gears.
Pros: Nice wide angle lens for the price, and with rebate the deal is even better. Seems to focus quickly, and is reasonably sharp from f8 up. Great for HDR shots,and Adobe Camera Raw and Lightroom 4 already have a profile for this lens to adjust for the barrel distortion.
Cons: Could be Sharper at lower f-stops. Lens cap doesn't like some polarizing filters(doesn't stay on), but no biggie. Chromatic aberration can be strong but the new lens correction tools in either Lightroom 4 or Adobe Camera Raw can eliminate that problem crazy easy. You have to have to do a little post work with this lens to make the pictures perfect.