He is just a guy that trained magic and studied technology, yet that made him strong enough to defeat omnipotent beings a number of times.
Marvel writers are always going on and on about how Latveria loves him and how he is an amazing ruler, even though in the past we have seen him killing innocent civilians from Latveria.
Reed and Sue are happy with him raising Valeria, even though this is the same guy that brutally tortured their other child and has tried to kill them hundreds of times.
Marvel wrote an event basically to tell the readers that the only good Universes in the Marvel Multiverse are the ones ruled by Doom. Like, if a Universe isn't ruled by Doom, then the universe doesn't survive. He is literally the only person in each universe that can save it. The heroes are irrelevant, only Doom matters.
Valeria loves him more than she loves her own parents, even though he is a guy that has tortured her brother and tries to destroy her family regularly.
Every time Dr. Doom is defeated, his defeat is retconned. "It was actually just a robot that looked exactly like me, but not me", which is terrible writing but his fans like it for some reason.
Every two years, he becomes omnipotent. And even when he is not omnipotent, he can just defeat any character, no matter how powerful they are, using "prep time".
Now even members of the Avengers seem to have forgotten that he is a villain and they treat him like a celebrity.
So, Doom is loved by his people, he is loved by the people he hurts, he is loved by the heroes, he is all-powerful, he can defeat every character using prep-time, he is canonically right and is the ultimate hero of every Marvel Universe, and his defeats are always retconned out of continuity.
Isn't he basically a rather bad Mary Sue? Why does his rabid fanbase refuse to see it? Do they believe that those things make him a well-written character?