The show's still got it. I'm scratching my head here, trying to try to figure out why people have a problem with series two.
The reason, as far as I can tell, is simply that the show dragged on too long. By this point, they're self-plagiarising and rewriting their own continuity. The show had a great ending when Kenshiro beat Raoh... except that it wasn't. They kept going on. Bear in mind also that there's another fat chunk of manga after this that wasn't adapted for the anime, although: (a) I liked that too, and (b) you could read the manga fifty times over in the time it takes to watch 152 anime episodes.
Me, though, I didn't have a problem with any of that. My not-so-secret weapon was to take three years to watch the show, taking big breaks between each story arc. It works. Seriously. I still like and admire the show even at the end and I don't think it's lost its mojo at all. If you inserted these stories in the early years, I think you'd be hard-pressed to tell the difference. It's still, paradoxically, one of the most sensitive, emotional anime of the 1980s. (It invented Manly Tears as far as Japanese anime was concerned and it has hardly a supervillain death that doesn't involve tragedy, a heartrending backstory and/or being cradled in the arms of your sobbing mortal enemy. It's inventing an entire genre's worth of tropes and playing every one of them more earnestly than you'd think possible, but that's what makes it so titanic.)
Mind you, we are still talking about a series where the hero is capable of hitting you so hard that he tears your skeleton out of your now-collapsing body. No, I'm not exaggerating. That really happened. The official French dub is a piss-take from start to finish, because everyone involved was so horrified at the ultra-violence. This despite the anime being toned down from the manga, e.g. in children's chances of survival.
It's no longer a show of greatness, mind you, but for me it lost that after the first story arc or so. Not enough stories about innocents and too much attention being paid to the inner lives of superheroes who almost all have the same personality. Different motivations, alliances and backstories, but all basically man-mountains with a weakness for tragic self-sacrifice and the conversational gifts of a garden snail. Imagine a black belt in "stoic" and the ability to make your head explode just by looking at you funny. (Again, not exaggerating. That's actually fairly run-of-the-mill for this show. The new big bad, Kaioh, is also a magician with the sorcerous equivalent of eye lasers and energy beams.)
It's iconic and awesome. Every so often, even here, it can make you stand up and cheer as Kenshiro saves innocents with blackly ironic ultra-violence. Episode 143, for instance. That's an insanely big rock.
How's it ripping itself off? Well, it's continuing the show's obsession with siblings, even though by this point it's getting a bit silly. How many brothers does Kenshiro need? Why should he care about someone he hasn't seen since he stopped wearing nappies? There's nothing as daft as "SPOILER is the twin sibling of a god" from the fifth story arc, but even so at one point I had to get Tomoko to draw me a diagram to satisfy myself that Hyou wasn't engaged to his own sister. (Sometimes, in this show, a so-called "brother" isn't a blood relative.)
It makes sense. It's not illogical. I like its use of Raoh, which is quite interesting (and, thank goodness, doesn't resurrect him). However it's possible to discern some chastisement of dead horses. They've also rewritten the past to make it work, so for instance the Shura origin of Kenshiro, Toki and Raoh contradicts earlier manga scenes that showed us their hometown, including their parents' graves. (The Shura arc's finale makes a big deal out of the mother's grave, which of course is in Shura.) As a child, was Toki's hair brown (series 1) or already white (series 2)? Exactly which brothers are and aren't blood relatives?
Let's also consider the Raoh-Kaioh similarities. Kaioh looks like Raoh, is metaphorically Satan (like Raoh), wears awesome armour while riding a monstrously huge hell-horse (like Raoh) and is the brother of heroes in his story arc, again like Raoh. He has the same voice actor as Raoh (Kenji Utsumi). He's even related to Raoh. There are enough important differences for him not to be a cut-and-paste (e.g. what he's prepared to do to Rin), but, well...
Specific stuff of interest in this story arc:
1. Major characters called Han and Leia, introduced at around the same time.
2. Noble pirates, which aren't my favourite trope. They fit this series, though.
3. "Use my body however you like." (Kenshiro to Shachi, episode 140. No, it's not meant to have those overtones.)
4. Shachi's an extreme example of this show's fascination with the borderline between hero and villain. He crosses that line on a regular basis, although after a while his allegiances become clear. Sometimes I hadn't the slightest idea what he was planning and thinking.
5. Rin is a huge part of this story arc. Almost no Batto, though. (It's set in the country of Shura and he's been left behind in the land of fewer psychopaths.)
6. Shura itself is quite interesting for a while, until it fades out of the picture as the story arc narrows in on the superheroes. This is a country of culturally evil killers, which can only be reached by crossing the ocean. (China? America? Japan itself, in the Edo period?) They're also staggeringly arrogant. It's illegal for men not to fight each other to the death and you don't even earn the right to a name until you've killed hundreds. Mercy is an alien concept to them. It's immoral not to be underhanded. It's not just that they're bastards, but that their entire culture has been bent into this shape.
Oh, and apparently death means nothing here because the loser gets revived in the body of the victor. I'm not sure how literally we're supposed to be taking this, though, and I might have misunderstood something. Anyway, all this is terrifying and I'd have loved to see the show engage with it on a deeper level than "kill the evil bastard in charge". In the end it doesn't, alas.
My favourite silly fan theory, incidentally, is that the "nuclear war" wasn't one. The show's clearly post-apocalypse, but what if the devastation was actually beyond-Kenshiro martial artists fighting each other and turning the planet to rubble?
It's the end of a very long series. If you've got here and you haven't been spacing it out as I did, you'll probably be dropping from fatigue. That, to me, explains a lot of the popular reaction. Personally, though, I still found it impressive and I think it still has the insanely gory, tragic, agonised heart that it's always had. The self-plagiarism is a problem, but less so if you can forget about the rest of the show and watch this as a self-contained story in its own right. It's still got that awe-inspiring faith in itself, even as it pushes its story material beyond even self-parody territory. Kenshiro is a hero so powerful he can beat supervillains even when technically dead, because his heart's stopped. He can step in the path of a speeding train and stop it with his fingertips. He must have killed tens of thousands of people, all in insanely disgusting ways, but he'd cry his eyes out over an enemy or a child.
Still magnificent. Of course it's the anti-matter opposite of subtle, not to mention a bit one-note and wearying if you're not in the mood. However there's nothing else like it. I disagree with the nay-sayers, obviously.