Old tech vs. new tech. -- Live View, Dust Delete, larger screen, larger files, weather sealed hotshoe, 1080p video, Digic IV, etc.
I, and a bunch of others, switched from a 5D to a 1Ds2, and I can't say that I regret it. A larger screen would be nice, but, I usually just carry my Epson P3000 with me to shoots if people really want to see the pictures. The two button menu change function takes a few days to get used to, but, nothing crazy. All in all, yes, it is a bigger brother to the 5D classic.