I tend to lean towards the "disappointingly soft" end of the opinionmeter. f4 or no - there's not one picture in the whole group (and I've studied these for a couple of days) that looks really sharp.
Being a Sigmaholic I tend to give them the benefit of the doubt. Is it the body? Need MFA? Bad first copy of the lens? Who knows. That wall picture for instance - at f4 it should be sharp, and it's not. That's almost as bad as my EF 24-105 f4 IS. Well, it was - the lens performs much better after MFA.There's nothing in that Rose picture for instance that looks as sharp as I would expect from any lens I'd plop on my camera. A few spots come close - but not really. I'm also not seeing any evidence of front of back focus.
I was really hoping Sigma would knock it out of the park with this one, and who knows, they still might. It could also be it performs the same as the Canon counterpart for less money - which is pretty much what I'm seeing here. Like I said, I'm going to give them the benefit of the doubt here and see how it shakes out from all the sites.
The rumored 24-70 f2 OS is the one I'm waiting for!