This is a list I have compiled of changes between the original Naxx and new Naxx. I have taken a long time digging through archives, interviewing old raiders, and using personal memory to make this list. It has a lot of info regarding changed things (And still probably missed some).
Considering the time and effort I put in to it, and how many changes it lists, down to the minor details, I believe it warrants it's own page.
EDIT: It needs a lot of cleaning up still, I'll start, but I am not to great at editing wiki articles, so someone else should probably clean it up a bit.