The Retreat experience on E-class ships is a great product. So good in fact that Princess copied it on the new Sun Princess and soon-to-be launched Sky Princess. The Princess Sanctuary cabins come with their own restaurant, sun deck and lounge (sometimes).
The difference is that Princess has some balcony and mini-suite cabins that are part of the Sanctuary Collection. Book one of those cabins and get “Retreat”-like amenities for a much cheaper price.
Has Celebrity thought about testing this on one of their ships?