We have cruised with Celebrity before and chose the Constellation because we like the ship, it was a very good itinerary and, at the time of booking, there was a good deal on Aqua Class inc. drinks package and gratuities. Our stateroom was clean, comfortable with plenty of storage and the bathroom was well stocked with toiletries. Servicing of our stateroom didn't start until the cabin stewards had delivered breakfasts which was disappointing.
Re dining - the buffet was well staffed, tables were cleared promptly and drinks service was good. Queues at the various food stations were generally short. There was plenty of choice but the emphasis on cooked dishes meant there was little in the way of cold meats, fish etc to go with a salad. The main dining room was very well run with plenty of tables for 2 and excellent service. However, we noted that the quality of the food has fallen since our first Celebrity cruise in 2012. We tried the Blu restaurant a few times but were somewhat underwhelmed - the service was not up to the standard of the main restaurant where the menu choices were often more appealing. Can't comment on the other food outlets at we didn't use them.
Regarding entertainment, the theatre offered a varied programme of production shows and guest artists. While not everything was to our taste, the shows were invariably of a professional and high standard. The singers and dancers were the best we've seen and the 'aerilistes' were terrifyingly good. Music around the ship varied in standard although the group Casablanca were outstanding with an excellent vocalist.
The cabin is big enough and the bathroom is adequate. Some might find the shower a bit cramped. Decor was light and bright with good lighting. The balcony was just big enough to accommodate 2 chairs and a small table and being on deck 9, always shaded by the overhang of deck 10 above. Anyone wanting to sunbathe in private would be disappointed.