To be honest, largely speaking, everything post [S] Cascade is actually incredibly frustrating to me, Epilogues and HS:BC included.
The retcon itself only exsists as a result of the issues that plagued Homestuck's writing since the beginning. Hussie's inability (or perhaps unwillingness) to tie up loose plot threads before introducing new (often worse) ones is a huge shame, given that they have a real knack for writing interesting and complex character relationships.
The first pitfall I think was that Vriska having any relevance to the Plot after Terezi killed her was a HUGE mistake. Hussie's obsession with everyone's least favorite character (joking, I actually liked her quite a bit up to that point) being the "big hero" is probably the thing that solidified my lack of interest in the comic beyond that point. Bringing her back is a good character moment for Terezi, sure, but it's not enough to completely demolish the trajectory of the comic just so Hussie could resurrect their favorite blorbo.
That said, there's a lot of cool shit in Act 6. I love the Nobles, I genuinely wish they'd gotten better writing overall. Caliborn is a Heel and I like it, Callie is A GIFT and I think easily the best late intro character. The Dancestors are just. Fine. the story didn't need them to exist I don't think, especially considering Meenah literally is just a teenage version of one of the main Villians of the comic, with literally no personality changes, and that is so redonkulously over complicated that It honestly deserves an award (a heavily artifacted star that just says "goog jorb" in comic sans). Overall though there are a plethora of characters who go underutilized, like Bec Noir who literally vanishes from the comic all but entirely until [S] Collide.
I have a VARIETY of qualms that I think are symptoms of this larger issue:
Gamzee is boring after the initial shock wears off, Aranea's entire subplot is subpar, and everything to do with the character Andrew Hussie is just. Not Great. Crocker Teir Jane COULD have been cool, but it feels like it's out of line with her character up to that point given that she literally KNOWS that Crockercorp is evil by the time she puts the damn tiara back on. Roxy being the actual leader of The Nobels session is a cool plot point that is SERIOUSLY underexamined, and don't get me started on [S]Game over, the fact that literally like 14 people with LITERAL GOD POWERS couldn't beat The Condesce is SERIOUSLY underdeveloped.
I think, that because of these overarching issues, The epilogues are largely Kind of Terrible. I read them in their entirety when they came out and I was more disappointed than anything else. I don't think they were written carelessly, but I think they were intentionally made to emphasize the parts of the comic that the vast majority of the fanbase (myself included), didn't like very much. they read like bad fanfiction on purpose, sure, but honestly, that's a really disingenuous and kind of cruel way to interact with a fanbase who adores a work you made. They feel like they were written Maliciously, and given that they happened THREE YEARS after the comic wrapped up is just the shit icing on the garbage cake.
HS:BC has the lifeblood of good Homestuck, but it didn't stick the landing, in spite of the fascinating and honestly kind of compelling story it's trying to tell. I think the new crew is doing better, but the ill will that pervades BC's origin and the fact that it's just downright BORING for the first 100 or so pages makes it not worth my time, personally.
Dirk is one of my favorite characters in The original comic, and the way he gets turned into a Caricature of his worst traits because of "fate" or whatever is super frustrating to me, considering the idea that Homestuck is a story deeply concerned with meta-narrative. Dirk is a character who wants to ESCAPE what he's "supposed" to be in parallel with Dave, "I'm not a hero" thing. and BOTH of those character choices are thrown out the window in HS:BC.
Overall, HS:BC and the Epilogues' obsession with making everyone the worst version of themselves is deeply cynical and is a very flawed way to continue a comic that is ostensibly concerned with growth and hope and becoming a better version of yourself. HS:BC is NOT good and I'm NOT a fan.
Also, change you know who's name to Tiffany Longstocking Harley, drop (or SERIOUSLY REWORK) the Rose cheating on Kanaya subplot, and she's the best character in HS:BC by FAR.
Casey Jarmes has a pretty good video essay that does a much better job of explaining some of my key gripes with the comic called "What Killed Homestuck", and it's pretty good in my opinion. They also have one about the Epilogues, but it's mostly just a recap. Though their insight is certainly interesting, it's like 3 hours long.
Soapbox Over, Kasper Out.