This is the best general purpose zoom I have had (of course I have never had a 24/28-70 2.
. Still, mine seems very sharp all around on full frame. It appears there are a lot of variance with the production, as some report excellent results and others report getting bad copies. (Either that or the bad reports are just people being overly critical and going into it with a negative mindset because it is not the 2.
Although I use it mostly at 24mm, here is a recent shot from Carlsbad Caverns at 99mm. Since you obviously cannot leave the narrow walkway in the caverns, this shows when the extended reach (beyond 70mm) comes in handy. This is the unedited JPEG, other than downsizing.