Whoa whoa whoa! That's a lot of stuff being skipped! I did read ayyo's Higurashi and the Jewel for Onikakushi-hen, so I think I have a better feel for the things the anime skipped in that arc... though I thought Mion admitting she spiked the riceball was a pretty significant thing to skip. I was wondering if that was just his imagination or what. Overall it doesn't seem like too many significant details were skipped.
As for Watanagashihen, the thing I was most surprised to see you mention was Rika's death. So that scene only happened in Meakashihen, and instead she was TORTURED in Watanagashihen?? This now clears up why she knew that Mion/Shion was a 'sadist' when she decided to kill herself instead of letting herself be tortured! The doll scene is also a pretty big thing to miss out on, but I already knew about that so I'm not as surprised ^_^ (But why did Oishi ask Keiichi if Rika had diabetes? Did he discover some substance in her body after her death, perhaps from the syringe?)
Tatarigoroshihen seems to have missed out on a lot of things; fortunately much of it was explained in the TIPs (like Rina's death and its significance, and the interview) or in the episode threads by gameplayers (like Keiichi's "KOOL" mode, which I really wish was animated). The epilogue was poorly done as stated, and I'm still confused as to how the gas disaster affected the nation, or if Oishi/Kuma really did die or whatever (I thought Oishi disappeared, but he reappeared in the 4th arc, which I thought was a sort of 'sequel' to Tatarigoroshi? Guess I'm wrong on that). And I still don't understand how Rika died, but perhaps that will be explained in later arcs. Like you said, I thought this arc was the most poorly done, even though it had more eps than the last 2 arcs
When I watched it with my friends, we all wondered aloud why Keiichi felt so attached to Satoko in this ep.
I thought Himatsubushihen was pretty good... it basically provided more clues to the table, kind of like one really long TIP
And from what you are saying was left out, doesn't seem too many significant events are missing.
Hm, I'm kinda divided on Meakashihen. True, it seemed like the anime missed out on many things, and the animation quality really made a nosedive, but I felt like much of it DID answer questions from Watanagashihen. Thankfully much of the missing material is available in the TIPs, though the doll scene and the epilogue missing truly is a disservice to fans. Leaving out the Mion<->Shion thing was kinda weird too, but it didn't really affect the anime too much (as in, didn't leave any plotholes really).
Oh man, the needle in the ricecake wasn't a needle at all?? It was tabasco sauce?! How could they leave out details like this
Oh well, at least I know now haha. And yes, I agree that the meeting between Rina and Rika seems pretty important. But what about the scenes referred to in ayyo's summary, such as Otaka coming to fight Oishi or something. This supposedly is important in future arcs, but who the heck is Okata?
Man after reading out all these things that are missing, I wish more of these things were explained (I know a lot of these things were explained in forums here, but for instance this is the first time I hear that it was tabasco sauce inside the rice cakes :P). But thanks for your in-depth response Lostblue (and all the other analyses and translations from Kj1980, Sushi-y and yourself).