I'm sorry you didn't enjoy NCL as much as you have on other lines. It can be a matter of timing and personal taste. That's why it's great to have so many choices in cruising. I hope your next cruise, on whichever line you choose, is more enjoyable.
For me, NCL has been my overall favorite line. I love the Freestyle concept, which now has spread to most lines, the diverse entertainment and multiple restaurants. I also budget for the additional charge restaurants. For an additional $100/pp you can have one of the best dining experiences at sea.
I personally found Epic not to my liking. Not in what was available in the way of food or entertainment. I just didn't like the ship itself. The layout, crowded pool deck, traffic pattern and cabins were the least favorite of any ship I've sailed, and I've sailed a lot of them.
Book another cruise on another line and enjoy!