I went through three copies before I got a good one. The good one was great. But I didn't enjoy Canons attitude as they kept saying a bad lens "was within spec". I hate that term.
Two drawbacks I found with this lens was the softness from 24-45mm and its slow f4 max aperture. I rented one for a wedding to try out and after 30 minutes use at a reception it was back in the trunk of my car for the rest of the wedding.