Conclusion: This lens produces soft images, I would be hard pressed to label it an L lens. I would think it would work well for taking photos of your kids while at the park, the IS and zoom lens will come ln handy, and even though the images will not be that sharp, they will be acceptable photos that the family will enjoy viewing.
Conclusion: This lens is built relatively well, and performs relatively well, although I am very much surprised with chromatic aberrations which are too high compared even with EF-S 17-55/2.8, which is not L, and has worse build quality. Was taking images side-by sude with these two lenses (as well as with 70-200/4L IS USM and 100-400/4.5-5.6 L IS USM, and this lens was the significant outperformer.
Conclusion: I have used this lens with great satisfaction until, after about 3 years, it broke down completely in the middle of a shoot. It turned out the diaphragm needed to be replaced at considerable expense. A little internet research revealed that this is a known problem with this lens, although there has been no acknowledgement of that from Canon. I am a long-term Canon fan (40 years!) but I have to recommend avoiding this lens until its flaws have been corrected.
Pros: great image quality for a zoom, smooth quiet operation, nice range for a walkaround lens
Summary: The build quality of this lens is excellent. The Canon EF 24-105mm f/4 USM L IS is surely one of the better standard zoom lenses for full format EOS DSLRs but it's not perfect. The resolution figures are generally very decent except for a pronounced border softness at 70mm @ f/4. Neither distortions nor vignetting are something to rave about at 24mm although these are no real issue at other focal lengths.
Conclusion: I've had this lens for about a month. Overall, it's alright, but certainly not as good as everyone else is saying. The lens isn't very sharp and often white will "glow" a little bit and bleed into black lettering, for example. My lens was manufactured in May of 2011, according to the serial code. Could have been a bad batch--the IQ is often ok but not great.
Conclusion: I tried one of these lenses about 3 years ago and ended up sending it back. I really wanted a lens with this zoom range, so decided to give it another try. For an "L" lens, this one is dissapointing overall. The build quality reminds me of a cheap kit lens. It just doesn't seem solid like all my other L's. Colors seem a little more muted and less vibrant than my other L's as well.
Pros: Reasonably Sharp. Very Useful Zoom Range.
Cons: Overall Build Quality Seems "Cheap". Lack of Weathersealing. Colors not as Vibrant as other L Lenses.
Conclusion: This lens has all characteristics to make it an all-time on lens, but it really sucks. Why? The colors are muted and dull. No light flooding of the images. I moved from Minolta 7D to Canon 5D Mk II and did regret the move alot the first 8 months, not knowing it is the lens(es). The images are sharp, but IQ is more. The images rendered by this lens miss any light flooding and get a wrong color nuance. I feel this is similar with the other non L Canon lens I own, 100mm f2.
Pros: Focal range, MFD, USM, IS, very sharp, solid, universal
Cons: Muted, lifeless colors, light quality is lost
Conclusion: I sold my 24-70 f2.8L and bought this lens. I thought the zoom range and IS would be great. I very much wanted it to work for me using it with my 1ds Mark II. Love the range, love the IS but very unhappy with the lack of contrast and sharpness that I had with my 24-70mm. So I ended up buying another 24-70 having great contrast and sharpness back and making 24"X36" and larger prints again. A friend had the same feeling about his 24-105 and sold his.
Conclusion: I bought this lens to have as a good single walk around lens. I have to say I am disappointed. I read a lot of reviews and thought I was making a good informed decision. However, you can't go to 24mm on the Wide end, as there are dark corners at the widest point. You have to go up to about 35mm to get them out of the picture! This should be a 35 - 105mm rated lens, and not sold for something it cannot do. It is really a shame, as the rest of the range is solid.
Pros: Super-sharp images, Fast auto-focus, is is great