I'm one who is not at all impressed with the Millennium ships. A few reasons why:
Lack of lounges per size of the ship which makes for less options for those that are looking for variety of lounges and ambiance. Too few dance floors per the size of the ship. 2 dance floors on a 91,000 ton ship is pathetic.
peas-in-a-pod approach to the ships, the Century ships were all different inside
big flaws in design of public areas--observation lounge is too big and not separated into different areas, therefore it is inefficient. That's why Celebrity is changing it. Thellasotherapy pool is too public for what Celebrity envisioned it to be, leading to the fiasco for charging for it to now policing it trying to keep kids out of it. Too many shops. Michael's club was oversized for its purpose, thankfully they are now piano bars lounges.
Lack of a promenade deck that wraps around the back of the ship. Lack of overlook lounge in the front lido area, lack of lower deck space, lack of teak decking.
long wings in dining room on both sides before the main part of the dining room. People sitting in these wings feel isolated from the dining room.
No writing desks in the libraries, strange oversight, IMO.
These ships I think are the poorest designed 91,000 ton ships on the market. I don't care how elegant the decor may be, functionally I have lots of problems with this class of ship and hope Celebrity totally rethinks the next class of ship.