Season 5 is another season chockfull of great TNG episodes. In fact, it has what many consider to the best episode of TNG ever: Darmok.
Man, what an episode and what a concept. An alien probe causes Picard to live an entire lifetime in the matter of hours just so he can understand their long dead civilization. That's some pretty heady stuff.
And it is one of the rare episodes that echoes throughout the rest of the series. Picard learns to play a flute in this "lifetime" he lives and that shows up in subsequent episodes as a sort of short hand for the impact of the experience on him as a character.
Another favorite episode is Cause and Effect which features a very Star Trek twist.
Find the rest of the posts in this series here.