My first-ever Star Trek novel was published in 2001, a TNG novel called Diplomatic Implausibility, which was Worf’s first post-DS9 mission as Federation Ambassador to the Klingon Empire. It also served as the pilot for the I.K.S. Gorkon series of novels I did in the aughts.
For me, the strength of this novel lies with the characters and the various arcs they go through. At the beginning of the novel, Klag resents Worf a great deal, believing his position to be the result of nepotism due to his being a part of the House of Martok. However, over the course of the book, Klag recognizes Worf for the honorable man he is and they come to an understanding. There are some other great character moments in Diplomatic Implausibility, including an unlikely courtship between Leskit and Kurak which was a great deal of fun. Leskit has a terrifically sarcastic personality and his story was a joy to read.