I've just read through the previous post here and you guys seem very involved with this game.
I also just finished going through other forums and talked to my friends from 2chan and here are my thoughts on Umineko:
It's possible that there is an ingenious solution to everything and if you solve the mystery correctly you will definitely know that you've come to the right answer. If you still question your answer then you still have not guessed right. (There are some old Chinese mysteries that don't state the solution, but if the reader duced right he will know he's right by the hided codes provided by the author.)
Its possible Ryukishi07 wrote a "Purple Flower" story and the answer is irrelevant and that the main purpose was the entertainment of the story.
(edit:I think as some of the other poster said, putting aside the murders this gives us an insight on the touching and loving moments of the family.)
It's possible like the graphic novelist, Alan Moore, Ryukishi is simply doing a deconstructionist story on the mystery genre and fiction in general. Much like how Alan Moore deconstructed the superhero genre and ushered in the 1980's comic age of grim, gritty, metaphysical, and thought provoking.
It's possible that like the theme of Lovecraft's work, fear of the unknown is the central plot and understanding the answer would drive one insane.
"The essence of the Mythos is that the entirety of humanity is insignificant on a cosmic scale. The human world is but a fragile bubble in an infinitely vast and indifferent universe, isolated by great gulfs of both time and space. Though we consider ourselves masters of all creation, as a species our limited perceptions allow us to see only a fraction of the full range of reality... The search for forbidden knowledge drives many, this knowledge proves Promethean in nature either filling the seeker with regret from what they have learned, destroying them psychically, or completely destroying the person who holds the knowledge." If we were to understand the truth we would drive ourselves mad. I guess sort of connected to Lambda's idea of a human or witch becoming a Creator, the present mind would not be able to understand it and thus go into a state of non-existance.
Even if you come to the right answer, if you don't truly understand the moral it will not be relevant to the reader.
As for the Schrödinger’s Cat Box, as a person who has studied a bit of quantum mechanics I am a bit suprised this was added to a Mystery story (of course it's also fanasty) but I'm glad it's being used outside the academic world.
In the end it's just a game. It's for entertainment, if the reader enjoys it, good. If not, then move on.
Apparently the lines are tightly drawn on the 2chan and other Umineko forums. But in the end Ryukishi07 does not own the reader anything or any answer. He's worked hard to provide us with fun entertainment. At the same time we the readers don't own him anything. It's the readers that bought the game and make Umineko so popular. In the end both Ryukishi07 and the fans are in a situation were each provides aid to the other yet does not own the other anything.
Oh and one of my friends who claims he's close to solving everything claims the extreme form of the Knights and Knave argument is needed to solve the mystery.
Here it is:
Three gods A, B, and C are called, in no particular order, True, False, and Random. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a completely random matter. Your task is to determine the identities of A, B, and C by asking three yes-no questions; each question must be put to exactly one god. The gods understand English, but will answer all questions in their own language, in which the words for yes and no are 'da' and 'ja', in some order. You do not know which word means which.
In the end I think Umineko is a fun ride, though I still have to wait to play EP8 myself. But I think I will finish with a quote from the Zen poet, Seng-Ts'an.
If you want to get the plain truth,
Be not concerned with right and wrong.
The conflict between right and wrong
Is the sickness of the mind.