The 28-300mm reviewed by Michael Reichmann at Luminous Landscape. His verdict?
"It's big, it's heavy and it's expensive. All aspects of performance at the wide end of the lens' focal range are modest, though it improves to quite decent levels at mid and long focal lengths. I am certain that there are photographers who will find that this lens' performance meets their needs, and for whom its physical and financial challenges are acceptable. But for many photographers two separate high quality zoom lens may well prove to be a preferable solution."
Link here: http://www.luminous-landscape.com/reviews/lenses/Canon-28-300.shtml
"It's big, it's heavy and it's expensive. All aspects of performance at the wide end of the lens' focal range are modest, though it improves to quite decent levels at mid and long focal lengths. I am certain that there are photographers who will find that this lens' performance meets their needs, and for whom its physical and financial challenges are acceptable. But for many photographers two separate high quality zoom lens may well prove to be a preferable solution."
Link here: http://www.luminous-landscape.com/reviews/lenses/Canon-28-300.shtml