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.
YMMV: Martian Manhunter
Canon Discontinuity - The Martian Manhunter : American Secrets miniseries, a pre-New Frontier deconstruction of the Silver Age made in the early 90's. J'onn, with the aid of the then-retired JSA's Doctor Mid-Nite, uncovers an alien conspiracy that uses 1950's American uber-conformity as its cover, with cultural rebels and outcasts as La Résistance. It was referenced in an offhand way once or twice after, and was retconned out without a major time/space event by editors just forgetting about it.
Complete Monster: Commander Blanx appeared only twice in the Silver Age but he made up for limited appearances with not rage, or hate, but pure, cold-blooded sociopathy. For reasons known only to himself, Blanx restarted the war between the Pole Dwellers (Pale/White Martians) and the Desert Dwellers (Green Martians). Meeting his adversary, J'onn J'onnz in single combat, Blanx won through cheating and exiled him; he later journeyed to earth and tried to kill J'onn during his exile there, resulting in numerous human deaths. Where Blanx really crossed the line, however, was in his rule of Mars. Already dictator the entire planet, Blanx used alien technology to take control of the Blue Flame that provided Mars' only source of heat, and set the entire planet ablaze. When J'onn J'onnz returned home, he found his family and friends dead, his civilisation in ruins, his planet unlivable, and all Martians, Pole Dwellers and Desert Dwellers alike, on the verge of extinction. When J'onn confronted Blanx and demanded to know why, Blanx explained that he had been contacted by an offworld mining corporation that wanted to buy Mars, but that "according to the aliens' code, I could only sell if I were the last living Martian." Blanx did them one better, killing not only every Martian, but Mars itself, desolating the entire planet out of sheergreed and apathy. In one issue, Blanx altered the tone of the Martian Manhunter stories from light-hearted sixties fare, to introspective angst, wiping out his own people in the name of his checkbook, and leaving J'onn totally alone. In terms of utter soullessness, no Martian Manhunter villain has ever surpassed him.
J'onn's first enemy (in current continuity), his own brotherMalefic, was probably one of the worst. Malefic engineered a psychic plague that incinerated the rest of the Green Martian race out of nothing but spite and envy at being the only Green Martian without telepathy. The reason he's not a telepath? He committed Mind Rape, an unthinkable crime in Green Martian society, and was punished by having his psychic powers and memory stripped away. So Malefic committed genocide on his own race over a punishment that he wholly deserved. As if this wasn't enough, Malefic was so hellbent on ruining J'onn's life after the latter defeated him that he followed him to Earth and murdered Karen Smith, J'onn's (as Detective John Jones) partner on the police force. This was the last straw for J'onn and he threw Malefic into the sun. The saddest part about all of this is that J'onn was the only person who was ever sympathetic to Malefic because they were brothers.
Fashion-Victim Villain: Both Mr. V (who wore a business suit jacket, a T-shirt, and slacks) and Commander Blanx (in his green and sickly orange get up).
Fridge Brilliance: Vulnerability to fire. One has to wonder why later writers keep inventing contrived explanations for J'onn's vulnerability to fire. Mars is cold and has very little oxygen to burn things. Why wouldn't he be vulnerable to fire in a high-oxygen atmosphere like Earth's?
Because he's a Flying Brick and in most continuities he even has Eye Beams which are at least somewhat laser-like. An otherwise normal human from Mars might be more vulnerable to fire than a normal human from Earth, but J'onn can go toe to toe with Superman. And he's more vulnerable to flame than he is to heat.
Additionally, DCU Mars had a much more Earth-like environment when it was inhabited.
The weakness to fire is quite complicated, and has little to do with varying relation to physical factors. J'onn's brother lost the weakness when he was stripped of his telepathy, for example.
Really, though, most people are weak to fire. It's not that outrageous.
Newer Than They Think: Not many people know this, but Mars was fully populated in the Silver Age. The concept of J'onn being the last Martian didn't come until later.
So Bad, It's Good: Back in 1959, there was a story in which J'onn J'onzz goes up against a foe called the Human Flame... who was a schlub named Mike who built a "crime suit" that shot electric bolts and fire out of little spouts on the chest. That's right: Flaming Shock-Nipples of Crime! He dropped off the face of the earth for 50 years and was eventually brought back as an Ineffectual Sympathetic Villain in Final Crisis.
Uncanny Valley: J'onn's almost-but-not-quite human shape sometimes disconcerts people. (And this was the form he created to avoid scaring people!)