I'll tell you what I said to two librarians the other night about this book - "It's mostly incomprehensible, but the story is pretty good."
I had to read this for a school project, if you can believe it, and for the most part it was a pretty decent choice. Captain Jack Aubrey is a likeable dunce with a real knack for taking "prizes" (ie, capturing Spanish ships) and his sidekick, Dr. Stephen Maturin, is a charming intellectual who doesn't mind getting his hands and clothes covered in blood on a regular basis. What's not to like about these guys?
Nothing much happens in this book, but it sets up the extremely lengthy series to follow, where Aubrey and Maturin have many exciting adventures. Aubrey gets his first command, bumps into Maturin on the street and convinces him to be his ship's surgeon, and then away they float with their crew of assorted misfits, cruising around the coast of Spain, shooting cannonballs, and blathering away at each other in their incomprehensible naval lingo. I think I'd have been able to be much more absorbed in this novel if the publishers had taken the time to provide a glossary. As it is, they've included a lovely labeled diagram of the various sails on a ship, but nothing about the ropes, wooden beams, and other parts of a ship that are mentioned over and over again - let alone the various different types of ships.