I really liked the old mkI 24-70L for some of the reasons it was critisied for...unfortunatly by forum nerds and not real world users. The old mechanism was highly critisied becuase it was extended at the 24mm end, while at the 70mm the lens was at it's shortest. This had a number of excellent but unique features...firstly the huge and over sized hood worked really well at the long and short end. Most lenses, the hood only really works at the wide end and serves little purpose at the long end. Zoom burst shots were increadibly easy with this lens, pop the shutter on 1/6th second shoot and twist....easy. The changing balance of the lens actually helped this technique. The weather sealing was aided by the large hood and when on landcape workshops, other photographers who were using the 24-105 often commented how better the hood worked on my 24-70L.
The level of distortion at the 24mm end was very low for this type of lens. But the best feature was the as one got close to MFD at the 70mm end, the zoom breathing worked in reverse and added focal length as the focus got closer to MFD....which made it really cool for differential focussing and shallow depth of field techniques. When worked right, it was very easy to through the background out of focus by focussing on a detail which is close. For weddings, I could easily get by with most of a wedding using that one lens....that's versatility for you. Sure, there were sharper lenses available. But I've always found the mkI sharp enough, even withh 22mp.
The new mkII version has sacrificed all this for sharpness....and yes it's sharper, but that is all.
Anyone here tried the Nikkor version on a D800...I've heard it aint that great. most of the rave reviews of the Nikkor 24-70 were mated to the D700, which was only a 12mp camera.