Is an interesting and spot-on description.
I've likened O'Brian's writing to an artist creates a drawing where parts are quick sketches that blend into detailed realism then flow out to sketch again. If you've seen the drawing of a hand that is clearly just lines at the edge, then realistic in the center, you have the idea. It's more of a sequence of scenes than a through-written book. I hope that makes sense.
I do know that O'Brian's favorite writer, whom he credited with his development as a writer, was Jane Austen.
That said, I love the Aubrey/Maturin series--I've been through it a couple of times, including on audio,
Post Captain, though, is a bit of an odd-duck. It's like the first 60% is one book and the second 40% is another one. Jo Walton wrote a while ago that she thought it was because he realized, unlike in Master and Commander, that he was setting up a long series and tried to get the roots of as many complications as possible into the book and that it would have been better served as two shorter books.
I can say that the later books have far more unitary plot lines.