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?

@the_rayman: I completely agree.

You seem to have something against Doom. For example saying that all heroes love Doom is a bit of stretch. Hell most villains don’t even like him. Also in Secret Wars 2015, it showed Doom couldn’t rule everything and besides he has been humbled countless times like other villains.

And no he isn’t all powerful even with preparation. If he were then why does he end up losing god good every time he attains it?

Also what event are you talking about? Cause Secret Wars 2015 pretty much shows what would happen if Doom we’re ruler and he lost there too.

I just don’t see where getting most of this from.

Not really. He's shown to have lots of character flaws and a big inferiority complex to Reed.