Tomomimorgan!
You spoke my mind! I've read all the series you've mentioned, though I don't remember much for Marmalade Boy.
I'm pretty okay with Ayashi no Ceres, since all I care about is Ceres, Aki and Shiso Mikagi and I got them where I want them... or close to it
Fruits Basket... er.. actually I got to a point where I don't really care anymore and all I want was for the darn thing to end already (though there were certain pairings made me squeal madly with joy)
As for Candy Candy, I can't help but agree with you. And I'm pretty sure a lot of people find the ending unsatisfying because of what happened. I mean, they were practically meant for each other!
And Kakan no Madonna... heh, I can't say much without spoiling others but you echo my thoughts
Personally, there's a lot of pairings which I wasn't happy with, partyly because I tend to go for the underdog of the love-triangle (I usually root for the good guy who does everything but gets nothing in the end).
But just to name a few:
From Ao no Fuuin by Chie Shinohara:
Spoiler (highlight to view)
Although I was satisfied with the ending and the Souko/Akira pairing. I just want more development for Takao/Souko. He's her sexy, dark husband in the past (even though she loves another now), I don't think anything can rival his love and devotion for her. It must have killed him (yeah, he's dead, so?) to hide his feelings for her, knowing she could never be his again and it's not even his fault! I don't need much, just a prequel showing how they once were!
From Kanon by Chiho Saito:
Spoiler (highlight to view)
Kanon/Mikami >:-( I'm not a fan for incest but... god, I really wish for them to be together. I was so disappointed to find out their true relationship cause I really love all their interaction prior to this. They were practically meant for each other! X_X
From Red River by Chie Shinohara:
Spoiler (highlight to view)
Rufasa/Nefert! >:-( If only I could just shake him to his senses, dang it!! Nefert is beautiful, intelligent, spunky and full of life, albeit cunning and mischievous. And she actually likes him but no! He only have eyes for Yuri (and so does the rest of male cast) >:-( and look where it got them to... either they die or lose their throne!
From Utena by Chiho Saito
Spoiler (highlight to view)
Touga/Utena! Yeah, he hurt her in some ways, but I feel that in the end, he proved himself to be the most devoted one to her. I just wish Utena could see that he's the one for her. He'll never be her prince (she doesn't need one anyway) but he is the only one that can stand equally next to her TwT
I can't think of anymore at the moment. I only name these two authors cause I've just revisited their books recently and realised that how unsatisfied I am at the pairings even though I enjoyed the stories immensely.