-Saki and Satoru were my favorite couple. Maria was shown to be more of a passionate fling then true love (granted they obviously cared about each other) and Shun met his demise before his and Saki's relationship could really go anywhere. Satoru and her were close to begin with, but they underwent the most development with each other out of all the couples. I like that their relationship is one that was actually built over a long period of time, it felt more realistic and genuine to me.
-Saki was my also my favorite character, with Yakomaru as a close 2nd.
-I get that Saki is the main character, so it would make sense that her relationships would receive more focus then the others, but I think the anime should have focused more on Shun and Sotarus relationship before Shun turned into a Karma demon, since it is portrayed as being an important part of Satorus character development.
On the other hand the manga has had no yaoi, and tons more yuri. So far, the manga has had about 3-4 full on sex scenes (all yuri) involving underage characters. So obviously the anime is a pretty big step up in terms of double standards for this and is more toned down for the sex (Don't think we saw anything other then kissing in the anime).
-As well as underage hentai, the manga also shows quite a few death scenes that are much more graphic then in the anime (pretty much at Gantz level if you've ever read the manga for that)
-The anime had a pretty toned down art style and feel to it in comparison to the manga, in which characters are much more over the top and quirky. As a result I felt the anime was easier take seriously and look at realistically, but less entertaining from one scene to a next when compared with the manga.
-The animation was 50/50 for me. I did like the simplistic style and aesthetic a lot, but at times it looked incredibly awkward and cheap, like in the kissing scenes. There were also times I was amazed by how stylish it could be, like in both ending credits and episode 10.
-Reiko and Shun are ghosts in the manga. They watch the events that happen to Saki and comment on whats happening in bonus chapters after their deaths (its incredibly cheesy and out of place, but lol neways)
-OST was good, but it seemed like they reused the same tracks a bit too frequently.
-The manga is not finished yet, its starting the final arc though.
-I too would like to read the novel and see how it differs from the manga/anime... Maybe one day.