There's a lot that Liveman has going for it. Aesthetically, it is about as Japanese 80's as it gets. The cast seems older than other sentai series I've seen, although that might just be from a misreading of the wardrobe (woooo 80's Japan!). But at risk of reading too much into it, this series seems to have put the Sentai team through the rigors of seeing some psychologically-scarring shit much much faster than usual, so I have to suspect that there is an element to them trying to reclaim what's lost. Given that the series opens up with a murder, betrayal, and a space ship full of their friends and classmates getting shot down and crashing into the city, which itself isn't that unusual for a Tokusatsu cataclysm, but what's unique is how they portray it. While nudging little bits of characters' personal lives and expressions to one another is a staple of Japanese drama, one wouldn't expect to see it as often and as emphatically as one does in Liveman. I'm often amazed that they were able to slipstream so much tragedy into a weekend-morning superhero TV-show targetted mostly to kids (I think...)

To be honest, it's not "adult" since that term usually seems to confer sexual themes and sexual-based romantic themes, at least in the American context where literally everything targetted at any demographic, teen bracket and above, has a minimum quantity of often extremely artificial "sexual tension" inserted at regular intervals. And that's usually it.
There's actually a lot of decently-regarded drama I've sat through which doesn't pull off tragedy with the minimalist elegance that Liveman sometimes does.

Remember when you were a kid and you had to read one of those classic "boy and his dog" books in elementary school? Like Shiloh or 'Ol Yeller? This show is like that. In fact, they literally do an 'Ol Yeller with a kid and his intelligent dinosaur pet. Although they barely stop short of the kid actually shooting the dinosaur, only to have the dinosaur die from exhaustion after the villains use it's mother's calls to stir it up into a blind (and enlarged) rage. So instead of dying from a mercy kill, both the Sentai team and the kid get to watch the poor dinosaur get tormented to death by the villains. The Sentai of course do what they can to stop it, but in the end, some buildings still got smashed, the dinosaur is dead, the kid is emotionally-scarred for life, the Sentai team has to bury another body and even though the Scheme-of-the-Week may have been thwarted, the villains basically come out ahead.

The underlying structure is basically that. One of the villains cooks up a classic, ridiculous scheme to impress the Big Bad, and the Big Bad gives the green light. The scheme is implemented unseen, which is actually where the show shines, because in that interim, it almost seems to be implied that what are originally supposed to be apocalyptic schemes, usually drift into being more like extravagant mind-fucks to pull against the members of the Sentai team with any collateral damage just being a "bonus" for them.

It'd be like if part way through Power Rangers, Rita specifically sent the Green Ranger down for the sole purpose of taking a dump in Billy's bed instead of fighting all the Rangers or whatever (it's been a very long time since I've seen that show). Then part way through, Rita abruptly changes his orders and has him fill Trini's zord with mayonnaise and maybe kill a few people at the school, while she personally lights everyone's grandparents on fire. Actually, it's not like that, nevermind. But the idea is, things oscillate from funny haha to wtf on a regular basis from episode to episode.

But I want to talk about Mazenda in Liveman. Actually, all of the three main villains. Ashura (the 4th) has so far been more for plot-purposes (raising the ante), but the original three villains are starting to seem more and more atypical over time. I wouldn't go so far as to call them "realistic" since they are, costume villains in a Sentai series, after all, but as costume villains go, they... behave like sociopaths playing a system and maintaining their personal brands. On the surface, sure, they play up the whole "look how abominable we are! Grrr! Humanity is dumb!" thing, but in no way have they actually escaped the realm of human behavior. They are the classic nihilist wunderkind archetype, or at least they think they are, but in actuality, they're just fanatics that don't want to admit that the rationale behind their actions stems from something as irrational as fanaticism as opposed to something more philosophically rigorous. This is one of those weird archetypes that's difficult to pull off well in sci-fi, since most people think it's unrealistic despite history being jam-fucking-packed full of people who were or are like that. After all, there's a reason it's so common. On the other hand, I suspect the 4th villain is a different case, as has already been hinted at, since he gained a great deal more from the Big Bad. His allegiance is much less based upon self-delusion and ideology, and thus: he's the one to watch out for.

Still, they occasionally show unexpected depth. Mazenda, in particular, is desperate to prove that she had rid herself of humanity but is clearly disturbed by the destruction of something pure or idealized. Go seems like somebody who just has a hard time with expectations placed upon him and underwent the most extensive physical change of the three. And Kemp just likes attention. Strip them of their villain status, they're actually pretty normal. I've had a hard time trying to figure out if the point they're trying to make is that these are just three people that fell in with the wrong crowd and drank too much of the Kool-Aid (in the figurative sense) or if this says something about youth forged in high-pressure environments (like the Japanese education system) being at risk of their otherwise normal issues exploding into something society can't deal with. I would normally say that this would be reading far too much into it... if it weren't for the part where they have peppered the entire series full of things that point to both. Including narration directly acknowledging it.

So, yeah: Liveman.

I still have another 2/3rds of the series to go, but I'm so far rather surprised by how unexpectedly serious it is. Then again, it was also 1988. And in Japan, they tend to define eras relative to the Emperor at the time, in terms of history, literature and by extension: attitudes. And mid-to-late 80's Showa Japan produced some real gems of recherché postmodern catharsistic weirdness like Takeshi's Challenge, Tampopo and the meta-saccharin sound of City Funk (an entire genre recently reborn as the source material for Vaporwave in the US). I'm sure there are better examples and probably some counter-examples, but it seems fitting that this series came from that era.