My experience is coloured by having cruised only once before, on a Royal Caribbean ship with more conventional ship design and cruising style.
The Pros for Norwegian Epic included the cabin (see separate cabin review) and being able to bring wine on board and pay corkage rather than (as with RCL) having no choice but to pay a heavy price for wine with dinner.
The Cons, for me, included the Freestyle format, which often seemed to mean Free-for-all, especially in the Garden Cafe, which was so hectic it was like eating in the middle of a large railway station. The food here was as good as you could expect from a buffet arrangement but in the waiter-service main dining rooms, Manhattan and Taste, I had expected better. The main central outdoor areas of the ship were very noisy and without a continuous deck circuit on any level it was not easy to find a quiet spot. It was also hard to find a quiet area in the public rooms without using a bar. The pools were much too small for a 4000-passenger ship and as a result overcrowded. The entertainment was high-calibre, but we could only get to Blue Man and Legends in Concert as other acts had sold out.
The cabin was spacious with many good technical features (TV, lighting, aircon control, phone, soundproofing) and a lot of storage space; it was a huge plus to have a balcony at an affordable price. Tea & coffee machine was also a bonus, though the actual tea and coffee were both poor quality, as was coffee throughout the ship. The controversial bathroom layout seemed to work well; the bed was comfortable but (because of the curvy layout) was not long enough for a 6-footer and the duvet material had balled badly up through washing.