It was changed because it was super 80's-ish. Problem is, they went way overboard with the changes. Instead of just freshening the ride up, they completely gutted it, got rid of half of the ride, and replaced the other half with REALLY simplistic themeing. The following update a year later made it better, but the damage was done - its less than half the length of the original ride and far less visually stunning. And the "lab" that follows the ride occupies the area that used to be track for the original. Where the old "lab" was is now private lounge space?!? The whole building is just misused at this point.
All of that said, if I'd never seen the original, I'd probably like the ride fine and I take my kids every time we go, and we all enjoy it and play in the lab afterward, so there you go. Those of us who went before 2000 just reminisce about what was. But in reality, everything is always better in our memories.