Yes yes yes!
I just had the last for one day, but it took me five minutes to realize it is the best lens ever. I have had a 24-70 2.8 L for the past six years. It was the only lens I had. I didn't need anything else. I just do studio and outdoors modeling photos, and this lens was always perfectly versatile for me... Until today.
I was expecting a little improvement over the old one, but I was actually blown away.
This really is the best zoom Canon is ever made. It is so sharp and so fast that It will never leave your camera.
The better news is that I found it to be about 10% brighter than the old lens. That means you won't have to pump up your ISO too high. I believe it is almost 2 stops brighter. It actually feels like an F2.0 lens.
I guess the new glass let's more light into the sensor and it is probably engineered specifically for the new full frame cameras like the 5D III and 1D X.
I know the price is a little steep, but if you can afford it, I assure you you will not be disappointed. It is worth every dollar.
Check out my two posts on the forum. There is a comparison between the old and the new lenses. You will be very impressed.