As a lover of super wide angle photography, when this lens was announced, I couldn't wait to get one. I think Sigma is making some of the best lenses on a quality/price level. I have the 30mm 1.4 and have just ordered the 105 2.8 Macro. I also have the Bigma 50-500 which I also love.
The other option for me was the 12-24 Tokina or Nikkor, but the Sigma won hands down. It's on my camera 90% of the time.
While on a six week holiday with my family around the world, I took some amazing photos in New York and Italy. Most of the 100,000 shots were done with this lens. It is crisp and capable offitting so much into the frame. The HSM is amazing and fast. Sigma provide the case and the lens hood. They are making some wonderful lenses and this is one of them. HIGHLY RECOMMENDED.