These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Many fans treat Kouji Kabuto as an arrogant, sexist Jerk with a Heart of Gold and a Chaste Hero based on the first anime series, in spite of later retellings and remakes mostly based on his original manga incarnation where he was less of a sexist toward Sayaka and less of a jerk, being nicer and tactful - yet also more of a pervert as befitting a Go Nagai creation.
Some fans think Sayaka Yumi is very stuck-up and bratty and more interested about showing off than saving the world, whereas other fans state she was simply an Action Girl had a very short supply of patience to deal with a loud-mouthed Idiot Hero and an aloof father cared for her but was Married to the Job.
The interpretation of the relationship between Kouji and Sayaka also varies depending on the fan. Many consider matter-of-factly they are the Official Couple, but some argue Kouji did not love Sayaka back. They base that interpretation on him teasing and mocking Sayaka constantly and showing interest towards any girl but Sayaka (Hitomi, Misato, Erika... even Minerva-X) and he was nicer to Maria in UFO Robo Grendizer. The former group of fans are quick to point out most of shows used the Chaste Hero trope back then - depicting The Hero like someone who is too busy saving the world to get too concerned about romance-, he baited Sayaka because he WAS a sexist jerk -and not because he was not interested in her-, , the Belligerent Sexual Tension was an Unbuilt Trope back then, the anime series showed plenty moments where Kouji cared for Sayaka, the Go Nagai manga (that Is the original story whereas the anime is an adaptation) did way more obvious he liked Sayaka, and in the Gosaku Ota manga they DID kiss. And they remind Kouji was more mature when he met Maria (when the first series began he was sixteen. In Grendizer he was already nineteen) and she was supposed to fill SAYAKA's role. And let's not get started with the ones think there was Ho Yay between Duke Fleed and him.
Boss is the Plucky Comic Relief to some fans. To other fans he is an unsung hero who always helps to the main characters and has nothing for his efforts in spite of some of his actions contributed to save the world. And depending who you talk to, he played straight or subverted the Hopeless Suitor and Stalker with a Crush with Sayaka.
Dr. Hell is a Large Ham and a Complete Monster wanted to Take Over the World to force the whole humankind to bow down to him, but in Shin Mazinger he was actually trying to save the world (although he thought conquering it was the proper way to accomplish that). Some fans actually feel Sympathy for the Devil, thinking it was unfair he worked so hard, scheming complex plans and strategies and crafting incredible scientific breakthroughs only to be defeated, crushed and humiliated over and over and over by a loud-mouthed, Jerkass Idiot Hero with a cool Humongous Mecha. People who know about his Backstory also tends to see him like The Woobie.
Yuri, Sayaka's cousin and Bratty Half-Pint is regarded by some fans like an insufferable, unbearable brat. Other fans see her like The Woobie, a poor little girl yearns for attention because her parents neglect her constantly.
Ascended Meme: The Boss saved the world joke is pretty funny when you realize that he really saved the world during the original series and sequel, even moreso in Mazinkaiser.
Despite all its flaws, the Tranzor Z dub at least had a catchy theme in its opening.
Complete Monster (Dr. Hell worked for Hitler. Before transforming Count Brocken into a cyborg, he stated he was going to use what he had learnt by experimenting with Jews in Austchwitz. And he grinned while he talked! His lackeys are not quite innocent, either)
Even the remakes (Mazinkaiser, Shin Mazinger, Shin Mazinger Zero) tend to focus on the Mazinger Z era, as Kouji gets put front and center while his successor protagonists Tetsuya of Great Mazinger and Duke Fleed of Grendizer are sidelined or completely ignored.
Harsher in Hindsight: In episode 17, Holzon V3 unleashed a chain of strong earthquakes left in ruins several Japanese cities and killed a lot of people. Forty years later, after a chain of earthquakes and tsunamis turned several Japanese cities in rubble, that episode looks even more tragic.
And Dr. Kabuto's manor, where he built Mazinger-Z, was located on the Forest of Aokigahara. Why is that relevant? Read and get creeped out. At least it seems clear why Juuzo chose that place: nobody would try to bother him or spy on him.
Also, the name Mazinger is similar enough to the name of pope Benedict XVI/Josef Ratzinger, that it lead to a flood of jokes. [http://nonciclopedia.wikia.com/wiki/Papa_Mazinga] Especially the film title "Mazinger vs Devilman" becomes extremely hilarious in that context.
The legendary HK subtitles are a goldmine of these. Outside of the aforementioned "we are entering the age of Fatso", gems include "don't be a cockhorse", "I AM MAKING THINKING NOISES HERE", and referring to Dr Hell's scepter as the Crabstick.
Nightmare Retardant: Count Brocken's appearance -a man whose head and body are split apart, and the former constantly hovers around the later, talking, laughing and screaming- was meant be frightening (in the manga he got Kouji reaaaly scared when he showed up for first time; and in the anime Baron Ashura initially thought it a bodyless ghost). Buuuut in the manga Boss managed grabbing his head when he got distracted, and Kouji and his friends played fetch and Brocken Ball (think of it like soccer, but replacing the ball with Brocken's head. And the only rule is everyone win. Except the ball). It was a tad hard taking him seriously after that. That scene did not happen in the anime, but on the other hand you had Brocken's head and body arguing with themselves -and the body punching the head-, or Ashura grabbing his head and instead of bring it back with the body, slapping him around...
OT 3: There are not many fans who do this, but some of them consider Kouji/Sayaka/Maria is a solution to the most important Love Triangle in the trilogy (nobody seems considering Kouji/Sayaka/Boss or Tetsuya/Jun/Boss, nevertheless. Poor Boss).
It is lampshaded in this Super Robot Wars Yonkoma comic: ◊
In fact, that characterization was more in line with his personality in the original manga.
What Do You Mean, It's for Kids?: Right like many Go Nagai works, Mazinger Z was aimed to children and young teens in Japan, but it was judged to be too violent to be seen by children in other countries like Philippines.