This isn’t a main character who’s a loveable rogue, or a sexy bad boy, or a tortured hero, or an anti-hero, or someone due for a redemption arc.
This is an evil protagonist. Completely and irredeemably evil, with no positive qualities whatsoever. So the story is about all the loathsome things he does.
I’ve come across two such manuscripts being offered for critiques, and they were… interesting. But that’s interesting to discuss, rather than to read. In both cases, I was so turned off by the protagonists’ amorality, casual murders, sexist attitudes and cowardice that I couldn’t read much further.
“The characters are supposed to be hateful,” the writers said in explanation.
Which is all very well, but hateful =/= interesting.
It’s certainly unusual to have the main character be a psychopath. It might even be edgy and dramatic, because some readers will be hooked by a character who tramples on all of society’s rules, who rapes and murders her way through the land without anything so cumbersome as a conscience.
The question is whether there’s enough of a line attached to that hook. If the character doesn’t have a solid, interesting goal, then the story might come off as gore porn. If the character isn’t smart enough to see the consequences of openly killing people (because intelligence is a positive quality, and she can’t have any of those), then the story's likely to end soon unless other characters take on the responsibility of protecting the psycho.
“Well, yes, he’s stupid on top of being self-centered and cruel,” the writers said. “But that means readers will be eager to find out how he's defeated in the end. He’s like Joffrey!”
I think one reason Joffrey never got a POV of his own was because he didn’t even have the fig leaf of enough sense to consider the consequences of his actions. It would have been difficult if not impossible for him to carry the story on his own.
And I've read books where I wanted the main character to fail - The Day of the Jackal was the first of these - but the MC usually had some quality that made them interesting (and I don't mean qualities like sadism and stupidity). The Jackal was extremely smart, competent and fearless. Hannibal Lecter was brilliant and sophisticated and had his own moral code, such as it was.
Another problem with characters who are Always Chaotic Evil is that they’re predictable. If you always know how a perfect saint will act in any given situation, then you also know exactly what a sadistic coward who hates women will do. This rarely makes for a engrossing experience.
Finally, if these characters are meant to be frightening—for me, personally, they aren’t, because they’re usually so over-the-top in their vileness that I find them difficult to take seriously. Whereas if the evil character has even a spark of humanity, one point of contact, it can make him much deeper and more disturbing. One of my favorite moments in Misery was when Paul saw what Annie might have been if she wasn’t murderously insane. In other words, he recognized that spark of humanity.
It didn’t make him any less determined to get away from her. But it did make her something more than just her madness.
Likewise, one improvement that Game of Thrones (the TV show) made to the books was to have Ramsay
There's room in fiction for characters who are roast evil with stupid sauce on the side, but if they're to take center stage and carry the story, they need more than just that to go on.