Recently my wife and age (both in our early 50's) had a chance to compare the Celebrity Summit to the Coral Princess as we has cruise on each during the 2012. It was an opportunity to do a head to head comparison.
We are Celebrity Elite but have noticed an inexorable decline in the product over time and wanted to compare that to the Princess product. We were on each in 2006 and found the Princess to be slightly better in the food department but Celebrity better in the wow factor department.
It is safe to say that Princess has remained good to very good in the food dept. As a comparison to say a Ruby Tuesdays on some things, other like their lobster, are better than that.
Celebrity, on the other hand has become more of a Country Buffet level of food. They consistently provide lower quality food, whether it's their too tough to cut, paper thin steaks, or the non sweet, rubbery lobster.
Similarly, Celebrity servers seem much more over extended. They never come back to ask how your meal is until it's too late to comment. Sadly, there really is nothing they can do about the food, except substitute one sub-standard meal with another.
I think this in turn has polarized them to guest complaints. Guest relations provides no service and becomes aggressive if complaints are offered.
As other posters have noted, for the money, you would be better on Carnival as Celebrity provides a first class experience only in their advertisement, and certainly not in the delivery of their product.
Grass on the ship is a great novelty, but I would rather have edible Lobster.