In the latest guide all the Celbrity ships fall into the top 12 in the world for their size and join QM2 and QE2 who are also in this group. So if they achieve this consitantly and only one ship was out of the top 12 in 2006/07 and that was Mercury they must be doing something right but we are all individuals with different ideas of what we expect of a cruise experience.
Its all a matter of personal taste and what you want from a cruise. For what you pay then I would say Celebrity give best value for money compared to its main competitors (P&O, Princess, HAL, and RCI for example) I have been on all their ships and even on the occasion when the pod system broke down, had a first class cruise experience. Their ships nearly always out perform others in the various expert assessments - but at the end of the day you have to judge for yourselfs.
I have cruised over 20 times - 2 times with P&O 1 with Celebrity and the rest with Princess. I have 2 already booked with princess for this year. I really do like Princess and now as Elite Passengers wont cruise with anyone else. Celebrity was nice but I felt there was something missing. Princess seem to attract many passengers from the USA and offers a very high standard of service - Celebrity does too but I do enjoy Princess best of all. The newer ships with Princess are really state of the Art.