While this post won't be posted until 2024, I read this book in 2023. I tend to prefer shorter books, but I think read like three or four of these 1000+ pages books in just a few months last year...
It's been many years since I read Tetsugakusha no Misshitsu ("A Locked Room for Philosophers", 1992) by mystery author, critic and philosopher Kasai Kiyoshi. That was the fourth book in the Yabuki Kakeru series, starring Yabuki Kakeru, a Japanese student of philosophy who solves baffling crimes and mysteries through phenomenology, i.e. the analysis of structures of experience and conciousness and who because of that, usually doesn't start solving a case until the end because he needs to see the whole structure in order to analyse it. It was also the first time I read a fiction book by Kasai (I had read a few of his critical works on mystery fiction), so it took quite a while for me to get started on my second. Interesting to note it also took Kasai ten years to follow up on Tetsugakusha no Misshitsu with Oedipus Shoukougun. I didn't pick Oedipus Shoukougun because I wanted to read things in order or anything like that by the way (I still haven't read the first three books in this series). In fact, I wasn't even planning to read a Yabuki Kakeru novel in particular. I had been looking for Japanese mystery novels inspired by Greek mythology, so I ended up finding this one. Like the previous book though, Oedipus Shoukougun seems to be written really like the fifth installment of an on-going story, and especially in the opening chapters there are segments that are probably spoilers for earlier adventures.
One thing to mention right away however is that 1) this book is long (more than 1000 pages), and that 2) Kasai likes to write about a lot of topics that are not directly related to the mystery plot. Depending on how much you can stand the latter, this can be a very interesting book, or an extremely long-winded one. I personally tend to fall in the latter category, and I certainly didn't enjoy the book as much as I perhaps could have, because there's just so much chatter about topics that didn't really interest me, but your mileage may vary there. In a way, it's very similar to the writing style Shimada Souji also has in his Mitarai Kiyoshi novels after the first few ones or something like Alcatraz Gensou, where he just starts writing about whatever topic that happens to be interesting him at the moment in a book, making them bloated works. In Oedipus Shoukougun, Kasai's pet peeve is of course philosophy, and characters will sometimes have extended discussions on philosophy. It's a topic that doesn't interest me personally, so I found these parts extremely tedious, but I guess some people will like it. Still, I think some of these discussions don't really make sense. There's a part where the closed circle situation on the island has been going on for a while, and they fear there's a murderer on the island. While some of them go search the house to see if it's safe inside, two others remain outside to wait for the clear sign. And what do these two do? They have a philosophical discussion. Topics range from sex to why a society condems murder, and there are also other discussions regarding the gay community and other topics, but I didn't really like the constant derailing that much, especially as they are only tangentially relevant to the core mystery plot (and certainly didn't need to take up such a large part of the narrative).
Because of the above, it also takes ages for the plot to finally move to Minotaur Island and to have the And Then There Were None-inspired plot to be set in motion (I have books that were shorter than the whole first section of Oedipus Shoukougun). Oh, for some reason this book also makes numerous references to how their situation resembles "a certain famous mystery author by a British novelist" and even spoils that book, but it never actually says the title. The same with the Ulysses references. Anyway, once it gets started, the plot becomes a bit smoother. After the first death, the caretaker disappears from the island with the boat... but is surprised by the storm raging outside, which overturns the boat. Which effectively traps everyone here on the island. But the following day, the murders continue, with more people being pushed down into the courtyard and other attacks being made on people. There's even a simple locked room mystery near the end, though that gets resolved pretty soon after it pops up. Overall though, the murders are fairly straightforward, and it's more a question of "Who could've committed these murders alibi-wise ?" For all the set-up regarding the Minosian palace, bull statues and other references to Greek mythology though, it's a bit disappointing these elements weren't played stronger, as the few links there are, are rather weak and not extremely important to the plot.
There are clever parts in the mystery plot but I think they kinda get buried by the amount of other things going and being told to the reader, and overall, I thought that as a closed circle murder mystery, Oedipus Shoukougun was just okay, with the potential for being a lot better had it been trimmed down and been focused more. A person obtaining a perfect alibi because of what he saw was done really well for example, and while not every part of the motive of the murderer worked for me, I think one part, the specific reason for why the closed circle was created, was an inspired move: it invokes a certain famous book perhaps, but here it is implemented in a far more natural way in-universe. Some of the clues pointing to the murderer were quite subtle too, allowing for Queen-like deductions, but I do think that due to few likeable characters and the constant derailing because Kasai wants to talk about something, the book overall feels tedious as a mystery novel, especially considering the enormous page count. If you just look at the mystery plot itself, it's a decently constructed story, with a few memorable moments, but it's not mind-blowing or anything.
For people who like their mystery novels to be a bit more pure literature-like though, I guess Oedipus Shoukougun might be interesting? It will certain tick those boxes better than a "straightforward" mystery novel. For me, this mode doesn't really work that well, and just looking at the core mystery plot, it's a good closed circle mystery with some genuinely good ideas, but in its current form, it just doesn't quite manage to capture me. So a book that will choose its readers, I think.