The Steerswoman Series by Rosemary Kirstein
It's been a while since I read this series, yet it has made a lasting impression on me. This is, in the end, a series about the power of the truth. The fantasy and science fiction tropes it uses are not the point. Even the "magic which is really science" idea, which was relatively fresh when the first book came out, has become a common trope by now.
Because the theme of truth moves me, I pay this series the highest compliment I can pay any book: just as I treasure the memories of reading The Lord Of The Rings aloud together with my parents, I intend to read this series aloud together with my children.
Throughout the series, the characters are well drawn. As with a good Leguin book, all of them are both individuals and members of their own different cultures, complete with ideals, prejudices, strengths, and weaknesses.
The action scenes are also excellent - high tension, yet never simply action for action's sake; they always advance the underlying plot, not just by getting the characters past some physical barrier, but also moving them in their quest for understanding.
Yet the series does have its flaws, and I think that book 4 is the weakest one so far (faint criticism, since the series is among my favorites). The structure of increasing discovery is hard to string out over seven books, and some of the later discoveries start to feel a little deus-ex-machina, as they lack an organic relationship to the basic setup from the first books. I don't want to spoil too much, but the exobiology has gone from the engagingly believable, and even beautiful, in book 2 to the somewhat "gee whiz" neat ideas in book 4. It's similar to, although at least more original than, the excessive tendency to include at least one rock-like "silicon based life-form" in any space opera.
For me, the power of the series is the institution of the steerswomen, and what that says about the social power of truth. The best scenes are when these ideals are tested, not by scientific ideas (which, after all, are more familiar to the reader than to the characters), but by new social contexts. These scenes are powerful and well-written, and they continue in this fourth book. I hope that Ms. Kirstein does not strain too mightily to continue the pace of "scientific" discovery for the rest of the series, and allows this aspect of powerful truth-telling to carry more of the weight. There are plenty of issues already to resolve, there is no need to have us continue to discover unrelated ones - I do not want a looming interstellar invasion fleet to appear in book 6.