Doom looms above them all as the closest thing to the Platonic ideal of a supervillain that the genre has ever seen.
He has tremendous pride and a firm sense of honor; he hides his face in a mask due to a disfiguring accident in a hubristic experiment; and he hates the leader of the Fantastic Four, the brilliant Reed Richards, because Doom has a bit of an inferiority complex. He’s motivated both by that neurosis and by an almost — almost — altruistic belief that he would rule the world better than anyone else.
That’s it. His gist is both elegant and internally consistent, as well as wholly unique. He isn’t a boilerplate desirer of riches, he isn’t an overcomplicated supernatural being, he isn’t a blindly murderous monster, he isn’t just the resentful rival of a hero. He’s his own thing, and he’s been a perpetual part of the Marvel Comics legendarium for 55 years.
Doom has been ensconced in a bevy of terrific stories over the decades, ones that have demonstrated what makes him work so well as a supervillain. The first and foremost factor is his nobility. I mean that in both a literal and figurative sense: He has a dashing and charismatic regal quality to his personality, but he’s also the actual sovereign of a nation. The latter factor makes him unique in the pantheon of top-tier superhero antagonists, and provides a fascinating twist on the usual archetypes for that canon: He has, in a way, already accomplished his goal of conquering — and, what’s more, he’s quite good at it.
When it comes right down to it, Doom is pretty much the perfect villain. He's a man of undeniably tremendous ability who could easily be the greatest hero of them all if he could get past his own ego and terrible jealousy. He's a man fueled more by his own perceived inadequacies than his abilities and this is what makes him so perfectly evil.
Beyond that, there's all of that ability- his amazing intellect, his powerful magic, and his peerless armor. He's a world leader with a powerful robotic army and he speaks in the third person. He's pretty much everything a villain should be.
Doom is the antihero of Marvel, along with Magneto, and would be very interesting for him to tangle with the resident one in DC, Black Adam!