Ship of the Line was one of the most well-rounded books I've read. It has great characters, a great plot, action, drama, TWO crews of the Enterprise - although Kirk's is completely hologram based, but still great nonetheless - and ties in Star Trek history nicely.
Character development was at a premium: You get great insight on both Picard and the reasons why is insane in the movie First Contact, and you get a peek at Kirk's sensitive side. We even learn more about the past and the present of Captain Morgan Bateson - who was briefly shown in the TNG episode Cause and Effect played by Kelsey Grammer. If the Enterprise-E was a character, we could say that he or she was developed as well since we learn about the ship's first voyage and the struggle between Picard and Bateson for command over it.
The ending of Ship of the Line leans toward anti-climatic - but it still is a fun and easy read.
Overall, this is an ALMOST must-read - but still missing that extra bit of "style" to push it into "Classic" Trek novel territory. Author Diane Carey has truly earned my respective with this book.