Just returned from a 15 day Celebrity Millennium cruise of the Panama Canal Westbound.
Celebrity was great as were the crew whom out of their way to make people happy. This is their job and they did it well.
This was my wife's and my first cruise so nothing to compare it with really. Overall, we really enjoyed it and will do it again. We wondered if 15nigths would be too long. We found around the 8th day that is was seemingly so but you adjust daily and found by the end, it wasn't long enough. Subjective really.
Our Cabin was great as was our steward. I would recommend at least getting a veranda when cruising. We spent a lot of time here just to remain outside and out of the crowds. With the deck overhang a few floors above us, we were completely protected from the rains.