I have this for you to read from Thom Hogan's website...
Originally Posted by RockNGoalStar
The 28-300mm seems to be trying to resurrect the 18-200mm DX experience for FX users. Let me remind everyone what that experience was: we were all at first impressed with the fact that the elephant could tap dance, but after attended a lot of performances, we decided that the elephant wasn't that great at dancing. As I wrote some time ago, the 18-55mm and 55-200mm DX combo could equal or outperform the 18-200mm DX in all respects but one: avoidance of lens changing. Also, you do know how much that 200-400 lens cost right? You might better off have a 300mm f/4.
I suspect we're going to find the same thing happens with the 28-300mm. Initially, there will be those that laud it because it "does everything," but they'll eventually get around to comparing pixels and find that the 24-120mm and 70-300mm combo do a better dance. And actually "go to 300mm." ;~)