So many wonderful things about this cathedral. I'm unlikely to add anything helpful to what has…read morealready been written so I'll simply add the following:
at 3pm on most days the friends of the cathedral offer a free (in French only) lecture/tour of the choir section of the cathedral, an area that is normally closed to the public. It's one of the best art talks I've heard in France, though I can only speak for the gentleman who led our talk.
don't miss the chance to climb the steeple and see the views of the building and of Amiens. You can only go in afternoons during the summer so make sure that you make time for it, and if needs be, book ahead.