I have only had this lens for a few days, but so far very pleased. Compact size and reasonably light weight for a lens with this range. Needs lots of light, but I knew this going in. Very good build quality and fit and finish. I like the option of twist or push/pull zoom and both are very smooth. AF is very fast and locks on well. It will hunt some with small subjects and cluttered backgrounds. Very easy to set up Custom Functions and update firmware with the Sigma dock. I am using this lens on a Canon 6D and am very pleased with this combination. A major drawback to some would be the lack of a tripod ring, but as I plan on using this lens hand held 95% of the time was not a very big negative to me. Will update this review later, but as of now am very pleased with this lens, especially at the price point.
A couple of shots showing original and cropped version. Taken from approximately 30 feet away with a Canon 6D. ISO 3200, no noise reduction.