Have to agree with Neuro.It is a decent lens, but not really an "excellent" one. It could use way more sharpness across the frame, especially in the corners. I wouldn't use the 24-105L for landscapes.
The current prices of the Canon and its real excellence will be a hard act to follow.
My copy needs a CLA buts is still a go-to lens for 80% of my shooting. What I really need is another for backup.
Sharpness is probably one of the things that Sigma is going to bring to the table.. And lots of it.
$500 for a Canon 24-105?? not for all of us!
If sigma bring more sharpness (and for a walk around I think the Canon 24-105 is fantastic as it is) to the table then it will be a real winner.
I'm wondering why Sigma would go head to head with that lens though? wouldn't the 50 1.4/2 be more obvious? unless they maybe they see it as a near future gap in the market.