We also sailed on the Epic last week and had many of the same complaints. We have been regular Carnival cruisers and we always have a fantastic time, but thought we would give NCL a shot for our 5th year anniversary. It seemed like they were severely understaffed, and those staff they did have seemed to all be brand new to the Epic. There were lines and waits for almost everything on board which got tiresome. Elevators were nearly impossible to get without a 5 minute wait. Bar service, while friendly and delicious, was super slow everywhere. They needed to have more beer carts around the pool deck like they had at sailaway, as many people waiting just needed a beer popped open.
We were really expecting to be blown away by the food, given how people talk up NCL (and seem to hate on Carnival). Besides the Tepanyaki Specialty Restaurant, the dining was severely underwhelming. Very monotonous fair on the buffet all week, most dishes in the dining rooms were just ok. Osso Buco in La Cucina was a stand out, as well as the garlic fried rice at Tepanyaki.
That said, we still had a great time (no such thing as a bad cruise!). The Thermal spa was amazing and was worth every penny. The main shows were also a step above what we are used to on Carnival, though their comedy club left a lot to be desired (Keith, the Comedy Club opener, was the most unfunny and uncomfortable act I have ever seen anywhere).
We may give NCL another shot in the future, but definitely not on the Epic. I think our next special occasion cruise will be with Royal Caribbean, which has always impressed us.