I got more and more unsatisfied with a 12-24mm third party lens (strong distortions, blurred edge) on my 5D mark ii, so I finally decided to upgrade to this extraordinary lens.
Very crisp images, limited distortions, and a remarkable fast 2.8 makes it a perfect landscape lens on the Canon 5D mark ii. I used it also on a party, well, the results where really cool.
The only annoying thing is the high pricetag, but still, it is worse every cent.