The original Ghost in the Shell is one of my all-time favourite sci-fi movies, and I was looking forward to this update.
And indeed, some scenes have been updated with lovely CGI graphics. The problem is that they don't blend in with the majority of scenes that are unchanged from the original. It feels like you're switching between two completely differently designed films. The two Kusanagis don't even look the same, which is distracting to say the least.
I didn't quite give up though, and tried to watch the original version included as bonus material on the blu-ray. The original Ghost in the Shell in HD would still be worth the price of the disc - only it turned out to be in un-glorious Standard Definition with plain stereo sound, and actually inferior to the DVD version I already own.
In conclusion: wait for the blu-ray of the original GitS. I wish I had.