Quite late to the party here, with the update released moths ago, showing than the release of the 5th book is on they way, so here I go.
First, I I surely find a lot of complaints anout the last installment, quite a lot on Google play, and saw some from here, but I’m gonna share my opinion about it, in some level I can agree, yet that doesn’t kill the book, quite the opposite, it was to expect that the 4th book was about the mysterious past of the MC and junko, which was teased and show small fragments of what was about, and and oh…hael, phew, personally beat a lot of expectations, more than I thought, was surprising to see those topics being touched in this book, and not much of a surprise considering the setting this put us on, fi you know about it that is, which long-story short, is gruesome and cruel and disgusting, yet isn’t for the sake of it, which is the reason of why cause so much impact.
My only grip and I’m gonna be brief, is the baron arc, that go Way to long, almost 1 1/4 book, and but not only that, but for the rest of book three and from time to time on book four, the topic is bring again, very reiterative about that point, have ‘talked away’ the the power who got very dependable of, which later is revealed than the raw talent of the MC was enough to beat their old sense and junko, and maybe a bit the shogi, but I actually enjoy it a bit, but even if was a simpler way to play it. 
Is funny than people have called this book quite a filler, and if we consider of how much this series has been compared with anime, is quite ironic to be honest because you know… What is anime without filler, that happens when is based from the original source material, manga… Yet I know there’s other factors anyway, returning to the main topic, it was pretty good, how all of this connected with every dot and just go full circle having and big plot twist in the lasts chapters, Or Who would thought than something as bizzare as the dream about the MC and the kid riding a koi fish, it was show the veracity of his prophetic insens… Well that shared look between them said everything. I yet about the trials and grief, it wasn’t done yet, with the kid and our lover/ex-lover and now one of our friends, lover or friendzone’d doctor who had a blind crush, is nothing but a shell for a OrJuki onna (had a lot of names actually) if that is what is, worse being a jorogumo, or on the top of the chain food, shinigami. whatever the outcome, so be it,that was an effective cliffhanger there. but and as a last note, I hope you have my doubts with Satsuma, gave me a orange light since he told about his prophecies and what had to be done.
As an overall, SoH is one of my personal favorite regardless of its flaws now just waiting patiently for the next release. 
Okay, so I gonna add other few things I forgot, going first with the most serious…
Probably one of the comparisons more uncalled for is comparing this 4th book with one of the most horrible and offensive and insulting books not only from modern literature, but as a whole and I’m going to mention it in another way 50 shades of metal and physical abuse aka 50 shades of gray, which in all honesty, is a serious stretch and I ain’t going to elaborate on this, because this isn’t about this book, only sharing a brief personal opinion of what I think about that argument.
Just as a trivial thing, and even more late and probably already mention, so I’m gonna do anyway, and is some references from other content in different platforms with the similarity of being a katana wielder and/or the ambiance on SoH when you input some of their names for your MC, not sure if those are all, but honestly I was expecting a few more like the swordfighter demon dog, or the samurai rabbit from dark horse, oh well…
Saito The lone wolf himself
Goemon The thirteenth generation of…er, I forget.
Batto A fitting name, that it is.
Jack Gotta get back, back to the past.
Aoshi Grand master of the Oniwanban—never mind.
Manji You don’t want to live forever, trust me.
Fuu Can you smell the sunflowers?
Ichi Being a poor ronin is bad, but being a blind one? No way.
Afro Just…don’t expect the hair.
Shishio Minus the bandage fetish.
Mugen I’ll take all you bitches on!
Baiken A grappling hook for an arm? No thanks.
Oyuki If only I didn’t leave my umbrella at home.
Balsa I’m still more a fan of swords than spears.
Ibuki What’s a girl hafta do to get some cake around here?
Kaoru My katana isn’t some wooden practice sword!
Ran A katana blade turning into ash? That’s just shoddy craftsmanship.
Ryo Me, a shameless flirt? I just like to tease.
Suzuka No doubt I’m an Ultra Class A assassin, too.
Jin I wish others tried to moderate their self-importance.
Hitokiri A fitting name, that it is.
Gintoki Freelance former samurai, at your service.
Tsubaki I guess I do work for the Grim Reaper, don’t I?
Kenshin Oro?
As a last thing, really this time, is about how SoH, reminds me to Samurai X (don’t remember the Japanese name, sorry), even if just a few things and mostly fro the MC if you are in a tamer personality (my choice of preference) to his protagonist, kenshi himura, and well, I’m well aware about this genre/shtick about the fearsome swordfighter/Samurai/Assasin who’s now in a more peaceful, mundane life, or as a vagabond, truth is, he is the one who introduced me to it, and personally one of the best, sorry for this rambling and thanks for reading.
). For example in book 2 when we chose to return momokos feelings, she goes away(for story reasons of course) and in book 3 when we have toshie or/and kohaku, we leave because a student died from our incompetence(emotional breakdown). Book 4 junko sacrifices herself to save us by cutting her/his arm off. Well with all said and done author I don’t know how will you resolve the if we have romanced in every book all this characters(like do we choose one in the end or harem route). I say that, because the story has this romantic regret build-up(for example if we are to choose older Masami from junko whom we romance in book 4 will his/her feelings just won’t matter or is it gonna be called out in book 5 or 6 whenever is the time skip?). English is not my first language so if l made many mistakes please bear with it 
!