Is The New Lens Worth It?

I would most definitely say it is! They have only just arrived in southern Africa (in very limited quantities) so field testing is still very new. Very few of them arrived in shops before Christmas in this part of the world. However, the build is similar to the new line of the STM's and the weather proofing is very obvious when extending/retracting the barrel. The images appear sharp and the IS is definitely up a notch. Remembering that the original lens is about 11 years old now and still going strong, I think we have another 100-400 vs 100-400 mkii scenario here where Canon's engineers have simply upgraded an ageing (but good) product and brought it into the 21st Century. They have done the same to some of their cameras, and also with good results. The new lens looks sleeker and is pleasant to hold, in line with several newer designs, and I can't fault that. I have attached a Hoya Pro UV filter and am using this lens in dusty, hot places (Botswana) to shoot wild life scenes, sunsets, bush scenes, poacher camp sites, game capture, insects, snakes, etc, where a wider angle is required as opposed to my 100-400L whichever is for longer range. So far, I found these two lens compliment each other  dry well. One of my colleagues still uses the original 24-105L (on a 6D) and is very happy with it, but the newer lens definitely has less vignetting and ca - as promised by Canon. I use the 7D ii and am very happy using this camera/lens combination. However, if you already own an original version of this lens and are happy with it and don't rely on it as part of your job, then don't rush off to purchase the newer version - wait a while until the price stabilises and your budget isn't so tight.