Pretty much the entirety of Chiru was amazing. I think my absolute favorite part was in ep 7, when the presentation went to the theater and the characters started acting as narrators. Umineko can drag at times, especially ep 4, but other than that, it's pretty much all amazing. It's a shame it's in such a weird spot, though: it's hard to recommend it to the typical VN crowd, since there are no choices (well, one) and it's so long, and it's hard to recommend to a reading crowd, since they probably don't want to sit at a computer and see anime characters for 100+ hours -- especially since it makes full use of the medium to present the 'fiction' sections. But what really appeals to me is that it never comes out and says what actually happens in the story; I have my ideas, but I've never seen anyone else say the same thing, so I dunno. I would also compare it more to an Agatha Christie novel than any other VN I've played, but maybe that's just me. And it is a pretty fascinating moral about truth vs. fiction in real life, like the idiom, "Where ignorance is bliss, 'tis folly to be wise."
Have you ever heard any of the... I'm not exactly sure what they are, image songs? Eirika's is probably my favorite: Intellectual Rapist. Obviously the OST proper is one of the big appeals, but I was listening to a lot of these songs for awhile after I finished it. It is a shame that any anime will pretty much either fall flat or be infeasible to make.