I've been very impressed with mine, since buying earlier in the year. It isn't a lens i use much, but I bought it specifically for shooting at Spa earlier in the year. I was so impressed with the sharpness paired with the 5dmk3 that I've kept it, though only using it for motorsport and rare nature trips.
I'd love to use it in the mountains for some tele goodness, but I can't deal with the extra weight to my kit bag for climbing.
For sharp longer focal length shots, you're onto a winner with this one!