We were on the Jade last month, which is a bit older than the Epic. Everything on this ship was well maintained, crew members were constantly cleaning, and painting, One ladies bathroom had two toilets that didn't flush, and I noticed that they were attended to later on.
I heard that NCL pays attention to what is posted here on Cruise Critic. Maybe that is why they never built a second ship like the Epic. Many people said that they would not book a cruise on it, including me, but others do like it.
If NCL is going to build more mid-sized ships, they should make exact copies of the Jewel Class ships. They do have fewer venues, but they are large enough to accommodate people, so reservations are not necessary except for the Specialty Restaurants. The pools are larger than those of the megas and newer ships. They shouldn't try to cram too much, because the venues will be smaller, and reservations will become necessary. When I'm on vacation, I don't want to be tightly scheduled.