incest is the very least of my favourite, but hell this manga excites me so damn much
I've seen more than one person say something to this effect, and I think it illustrates how good a manga it is, subject matter aside. It's just really well done all around, in art and storytelling and everything else. If it keeps up the same level of quality to the end, I really think it'll go down as one of the all-time classics of yuri manga.
I have nothing against incest in stories, but I'm only interested if it goes beyond shock/titillation value. As you say this is a fairly serious and very well written story, and that makes it really stand out because it is a subject that rarely gets that treatment.
But even beyond the story telling skill I find that I really like the specifics. I love Taiyaki's wry, low key humour (the Venn diagram was my fav, but lots of others), and most of all I find Asuka incredibly relatable (though all the characters are pretty good).
I've never been romantically attracted to my mother, but apart from that she is basically me as a teenager. Quiet, into science and mathematics, avoiding humanities, she isn't particularly interested in people (hates crowds!) and doesn't have any real friends (just acquaintances). She's not lazy, but she isn't motivated either; she succeeds in school, but mostly through intelligence rather than hard work. She over-thinks and analyses every action and interaction, but almost always just "goes with the flow" (the Miyuki arc is a good demonstration of this).
I never expected to particularly like a character who resembled myself, but I have a real soft spot for that earnest little would-be mother-f*cker (which I suppose brings us back to good writing, lol).