I'm a big fan of David Drake's Leary and Mundy series (AKA the RCN series). The description of the series typically calls it military SF, but when I hear that term, I tend to think of SF that's primarily focused on the details of battles. Oh, there are always a few battles in these books, but I tend to view them more as space opera (though I hesitate to try to draw the line between space opera and military SF).
Though Hell Should Bar the Way is a change from the previous books in the series. Those were told in their person, and primarily focused on the two main characters, Daniel Leary and Adele Mundy, much the way Patrick O'Brian's books (the inspiration for Drake's series) concentrate on his two main characters. But his book is told in first person, by a new character, Roy Olfetrie. He's someone who had wanted to be in the RCN, but had to leave the Academy when his father was disgraced for stealing money while doing naval procurement. He gets a chance to be a spacer, though, when Leary, assigned to a civilian mission of escorting diplomatic personnel, taken him on.
But things get complicated when Olfetrie refuses to listen to an ambassador who tries to get him to go against Leary. He's kidnapped, forced to work on a tramp ship which is taken by pirates, and then sold into slavery. But he works his way into a position of trust, then helps a woman imprissoned in the harem, and together they escape, with various adventures along the way. Leary and Mundy are therefore only involved in the story in the first quarter and last quarter of so of the novel.
It was fast, entertaining read, and I was happy to see some of my favorite characters as well as some new ones that I hope to see again in future books.
I recommend this series to fans of space opera and to fans of the novels of Patrick O'Brian.