I have been playing around with the new Canon EF 16-35mm f/2.8 II, and I will be doing some testing with it over the coming days. My initial impression is that not much has changed, unless you sweat the minute details. Probably the biggest change has been the filter size, as it moved from a 'standard' 77mm to 82mm. Since I rarely use any filter on wide angle lenses, this isn't much of a consideration for me. For example, polarizers at 16 to about 28mm or 30mm has very distinct polarized areas and non polarized areas in the same scene. I am not a fan of using UV filters on my lenses, unless I am headed to Namibia to photograph in extreme sandy environments. 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.