After cruising with Celebrity on the Equinox in the Mediterranean last August, we decided to use them again as we had a great time on that ship. The Constellation is not the Equinox, however. You can see the age of the ship everywhere, with rust stains from the pools to the all parts of the exterior, and the missing varnish on most the exterior woodwork as well as the un-appealing soiled deck chairs from layers of suntan lotion that were never cleaned off. The windows needed a good cleaning as well.
The staff, while very good overall, were not as crisp and sharp as those on the Equinox and in general it felt like a second-string ship in all respects. This is not to say it was a bad experience, because it was not, but it felt more like Carnival than the upscale image Celebrity prefers to market itself as.
Wi-Fi rates of .75 a minute are ridiculous (many of those on board the Constellation were using the free Wi-Fi of the Carnival cruise ship we docked next to in Cozumel) and for those buying balcony rooms, be aware they have an extended top deck over all the rooms - avoid Deck 9 and go with Deck 8 rooms if you can to get less of the 'awning' feel on your balcony. Cabins are small. Bathroom size OK.
Overall: Its time for this ship to go to dry dock and get updated.