I've sailed Celebrity and have another one of them coming up in February.
They have good food and a good selection in the MDR and a very good buffet (they have a pod kind of thing - pasta station, pizza station, sandwich station, salad station, hot food station, cheese station, etc.). And if you're into coffees or sweets, Café Al Bacio is not to be missed (it's my favourite thing about Celebrity). Their staterooms are set up well and have comfortable beds and good bedding. They have traditional evening entertainment (song and dance shows plus headliners). They also have a very good adult only pool area. The ship décor is generally understated and classy looking. They offer a glass of champagne or a mimosa upon boarding.
I do find them a little on the boring side generally (not too much excitement), and a stronger focus on the beverage packages (which leads to a higher focus on getting a drink and sitting somewhere - usually wherever there is live music gets packed).
We've done Bermuda with them twice (7 night cruises) and the Caribbean once (an 11 night cruise) and found those cruises not to be that much older of clientele. It was much more middle age, or newly empty nesters. A few kids on board, including several babies who were the apple of the crew's eye.