This is our third cruise and our first with Celebrity. We have previously sailed with Carnival and NCL. I certainly wouldn't consider us to be cruising experts, but after sailing with Celebrity, I don't have a compelling reason to go with another company. Our first two cruises were fine and we had no major issues, but our cruise with Celebrity was head and shoulders better than our previous two cruises.
Embarkation was comparable for all of our cruises. The staff on all three cruise lines was friendly but our Celebrity staff was definitely better than our other cruises. The food on Celebrity was better across the board. Specifically, when we did eat at the buffet, the food tasted better and was much fresher than our previous cruises. The common areas were very nice and much less gaudy than other cruise lines. Also, our cabin 7144 was bigger, cleaner, and more updated than previous cruises (all three have been with the same type of room, balcony).
I don't like to get hounded to stop constantly to get my picture taken. I know this happens on pretty much all cruises, but it was much less often and irritating with Celebrity. I also felt like I was nickel and dimed for everything with Celebrity. Finally, my wife and I are not what I would describe as "party people". The atmosphere on Celebrity is much more subdued which suits us much better. Others might like something different. For example, a Carnival ship left just before us. As they pulled past, there was music blaring and the cruise director was yelling over the PA system. Our departure was much quieter. :)