I believe that the small 'O' ships deliver an adequate level of entertainment on board. The main focus for most on 'O' is the fantastic destination's they serve on great itineraries. They are excellent at this.
And because of the smaller size of the ship, they cannot offer the level of entertainment that mainstream cruise lines offer, like sibling NCL, which offers superb variety, including full Broadway shows. As a destination focused cruise line, most passenger's retire early, to wake up early for a full day of shore excursions. The ship is indeed quiet on most late nights. But as the dailies posted above show, they do still have a variety of different entertainment, with the ship's own cast, as well as various 'guest' entertainers that are on for a show or two. And lot's of 'Big O Point' earning activities, that can be traded in for much better 'prizes' than offered on the mainstream cruise lines.