With any product there are constants and variables. With Celebrity the constant would be the Celebrity style and activities, the particular ship though it may be refurbished and redesigned in areas, the ports although conditions can vary at the ports. The variables are the crew and how they interact with each other and supervision, the Captain can impact the feel of the ship and the cleanliness factor, the weather, fellow passengers and the ambiance they create, entertainers.
I judge cruises and ships by variables and constants. A particular ship does not necessarily have good service and food, it is the crew and conditions on board that provides this and crews rotate from ship to ship. I remember seeing pictures of Suni on the Summit, for instance. I also try to evaluate ships, how they work as ships. And when I evaluate I look for things that cruisers use, whether or not I use them. For me, cruisers use deck space, various deck space. I never go into the pool but that doesn't mean that they don't matter because I don't use them. I don't use casinos but that doesn't mean the ship's casino content, design, do not matter. I can think of few ships that don't compromise something in terms of a ship feature. So, looking at the ship one can look at ship navigation; ratio of deck space and how it is divided from top to bottom of the ship; pool areas; evaluating dining rooms in terms of waiter station placement, placement of seats, traffic flows, waiter's distance to galley, placement onboard ship, etc.
Overall, when I look at the new generation of ships, I have a problem with public deck space, and I think Millennium ships are the worst in that the promenade deck doesn't go around the back. The addition of balconies to the stern have taken away navigation from a lower deck to a higher deck. It is now necessary to go inside the ship to get to a lower or higher deck area. Pools never seem big enough. I think ships with quiet aft pools are a good feature for cruisers. I think a variety of intimate and grand spaces fit different tastes. In terms of navigation there's a compromise between good navigation and inviting public areas, and sometimes what's best for the crew. Sometimes one of these has to be compromised.
The product delivery in terms of service, food, entertainment, can make or break a cruise. But there's a difference between judging a ship based on a particular cruise vs. how well it facilitates the style, function, and the variety of passengers one will find on its many cruises it sails month after month, year after year. My comments about ships, esp. Millennium vs. Century ships takes into account how well I think the ships work for a variety of cruisers, how much care I think went into the creativity and design of the class of ships, and how many details were changed or altered with each newer ship of the class. Any particular ship in a fleet is capable of great or poor product delivery depending on variables of their crews and which crew members one encounters and deals with on any given cruise.