Ep 6 is probably the worst Episode even without taking the ramifications to the mystery behind it. It's got a couple amazing scenes, and the rest is just sloooow.
Beginning of Episode 4...man. I had actually enjoyed every single part of Umineko up until that point. Every intro, it was all great. But that was just awful.
On a more positive note, the series does climaxes veeeeery well. The end of every episode kicks ass.
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Black Turtle did a pretty good job.