I've been rewatching Star Trek: TNG with my daughter (she's seen a lot of TNG episodes, but never watched it systematically until now).
We've reached s6, and that has some of the silliest episodes they ever did. It feels like that's when the momentum ran out after Roddenberry's death (perhaps he had been involved in decisions made for s5?).
Because we started to see a real lack of restraint in the writing at that point.