I had already watched the anime, which is one of the best I'll probably watch, I started this manga. The art is good beyond words, not only the cute girls (and boys), just look at those backgrounds!
I'm against using "yaoi" and "yuri" terminology in this work because (at least yaoi) are very specific names of specific genres (originally, "yaoi" means "nonsense"). They're (inexistent) "gay" and (too much) "lesbian" scenes, and they had a purpose. I would be hypocritical if I say I don't enjoy girl-on-girl action, but they are too long and too much, and it was embarrasing to read it on the bus; one of my friends asked me "what are you reading?" I replied "I'm still with the hentai manga I showed you the other day".
The downtone of Shun and Satoru relationship from lovers to good pals is a wrong choice (I would prefer to keep them boyfriends but not showing me their relationship graphically): when I watched the anime, I was horrified by that kiss between Satoru and Shun, but I understand that it had a purpose, and it was justified both by the social organization and the personal relations between the main characters, in fact, as an amateur writer, I feel jealousy of the author for this whole idea of the bonobos (including same-sex relationships). It's brilliant, he is a damn genius.
OK, that was too much whining about terminology and gayness. Let's move on.
I like the more joyous characters, specially Shun, Maria and Saki, all of them are less melancholic that the anime, even Mamoru is annoying (but still very annoying). Maria is more cheerful and aggresive, Saki is less frozen by revelation and more instantly shocked (this way she can act) and Shun is more charismatic and less gloomy (it worked fine in the anime nonetheless).
I read reviews about the novel that tells that it is very dark and cruel, the sex scenes unappealing, sad and ultimately unsatisfactory for the characters. I like how it sounds, I'm waiting for it.