There's something overgeneralized about statements like "designed for the mass market". There are segments of the mass market. Carnival and Celebrity fit different segments, have some overlaps and some similarities, have some differences, and the weight each passenger puts on what the cruise line stresses in their experience impacts their assessment of the products.
In a general sense, Celebrity is like the others. More specifically, compared to NCL or RCI, there's less noticeable selling of the product and the most obvious aspect of this is the minimal annoncement policy onboard Celebrity. There's also a more upscale tilt in the manner of service, presentation, ship appointments, passenger space ratio, ratio of servers to passengers.
The food is both subjective and inconsistent. It is very difficult to go on 2 or so Celebrity cruises and come back with a general conclusion about the food. And that's a Celebrity fault. So, on one hand people are overstating the quality of the food at times it is superb, at times very good, at times average, at times substandard. The knowledge of well-prepared, presented, and flavored food of pax also varies, many pax will say that what they like is great food.
Celebrity suffers from overpromising and underdelivering and many fans of the line giving people inflated expectations of the product. The product is quite good when looking at the overall value and bang for buck. But, for many pax, it is not a huge standout over other lines and it tends to shine in subtle areas--and that's when the product delivery is on.