didactic
adj.adj. describing something that is meant to teach or explain a lesson. It often feels a bit boring or too serious because it focuses only on giving information.
adj. intended to instruct or teach; having a moralizing or instructive tone. Often carries a negative connotation of being overly serious or lacking in entertainment value.
The teacher gave a very didactic lecture on history.
The book is so didactic that it feels more like a textbook than a story.
While the author's intent was to educate the public on environmental issues, the didactic tone of the final chapter alienated many readers who preferred a more nuanced approach.
From French didactique, from Ancient Greek διδακτικός (didaktikós, “skilled in teaching”), from διδακτός (didaktós, “taught, learnt”), from διδάσκω (didáskō, “I teach, educate”). By surface analysis, didact + -ic.