The original 24-70 appears to have better build quality (the new L's seem to be made of cheaper materials, no surprise from the last company to still charge for lens hoods), and the new 24-70 doesn't offer any feature improvements.
Actually, the build quality of the original 24-70 was very problematic. People who used this lens heavily learned that it needed frequent calibration, and the calibration was not simple. It required a trip to Canon or an independent repair expert. One calibration every year or two was about enough for me, but I heard a photographer claim he needed calibration once per month. I don't know that for a fact; it may have been a bit of hyperbole. But the lens definitely had something that would go out of whack with heavy use. At some point, you would find that it couldn't focus well any more. People who used the lens very lightly probably never got to that point where it needed calibration.
If the new lens is better in this respect, and needs very infrequent calibration, then it will be a HUGE upgrade for some photographers. The money (and downtime) saved on calibration will pay for the extra lens cost. And the added reliability, sharper photos, and peace of mind will be an everyday advantage. I am hopeful that Canon has addressed this one big problem of the original 24-70. I suspect that this is main the reason for the upgrade. Whether that is a fact, only time will tell.
I am definitely not in favor of keeping the build quality of the original: it just wasn't that good. And it was big and heavy and awkwardly balanced as it got longer when zoomed wide. The 24-105 had much better handling, so I'm glad that the new 24-70 II works more like the 24-105. Adding IS is not a big attraction for a lens in this focal range. I would rather that they spend their resources on image quality and durability. IS would be very nice, but wouldn't make it a big upgrade for me.