The stretch of episodes between "The Pegasus" and "Preemptive Strike" is among the weakest in the show's history, but "Lower Decks" is a very pleasant exception.
Despite some lighthearted moments, it's a serious episode - along the lines of "The Pegasus", "The Wounded" and "The Drumhead". Putting a guest actor in the headline role is always a risk, but here it works out great. We get a great supporting turn from Michael Dorn (go back and watch one of the 1st season episodes - hard to believe it's the same guy!).
Alas, there is a lot of mediocrity to sit through until we get to the series' final two.