Another change, albeit small, is that the autofocus on/off switch on the side of the lens is now much easier to switch on and off. If you have the EF 24-105mm f/4 L IS lens, you will recognize the new switch, as it has grooves that grab on to your finger. A huge plus if you are shooting with gloves on.
Here is a great review that has already been published on the lens.
Is the upgrade worth it? I have no idea. But I have a hard time believing this new lens is worse than my 16-35mm series 1 that it is replacing. I will be giving it a spin on board our Galapagos motor yacht later this week, though.