I have the 28-135 on a 1.6 crop camera. The lens is good, but not great. The range is very good, for group shots of 6 people or more then you need to get a distance away, but apart from that, it can take some nice landscape style shots (my widest lens is 17-55, I hired the 10-24, but found I used around 22mm most of the time for landscapes as it was easier to frame, but perhaps that is just me).
One downer (as someone has already mentioned), is that if you have the camera around your neck, and walk-around, the lens is prone to extending. However in use taking a shot I have not had this problem. Has a decent focusing speed.
The lens has done well for the almost 3 years I have had it, but I am now considering whether there is a lens like the 24-105 in quality, but with a bigger aperture. (and within budget).