I wish they add a little to their prices and have better AF. To me, a lens as sharp as anything is pretty worthless unless the AF can make that sharpness happen consistently. Almost all of my favorite shots of the kids are when they are running or otherwise moving quite a lot.
BUT, I love the turn Sigma have taken with all of their new lenses, they've released quite a few, consistently very high quality in (almost) all aspects, and I bet Nikon and Canon are scratching their heads and perhaps having a wtf-moment.. Love that. !