as a whole it’s really divisive. you either love her or you hate her. hear me out.
i think it all stems from her start of villainy: sunburst dumping her. what i think they wanted to do was give her a very identifiable start. everyone’s lost a friend at least once, so it’s something we can all relate to. it’s a double-edged sword though. because it’s so identifiable, it comes off as a very piss-poor reason to become a villain. a lot of people look down on her as a spoiled rotten self-centered brat and feel that it doesn’t justify all the very horrific and evil shit she pulled (even if you don’t count all the alternate timeline death and suffering, remember that trying to rewrite time in and of itself is still an unforgivably evil act).
i honestly think if they just hadn’t had the sob story to begin with and had just had her begrudgingly realize she’s destroying the world and gone on to accept twilight’s offer of friendship, it would have made for a much stronger character. the knowledge that a pony who is good at heart but has done such extreme things would have implied a start of darkness or series of events to make her that way, allowing a lot more people to accept it as reasoning for her evil behavior. before you say it’s too subtle for kids or whatever, remember they did that for discord too.
what really doesn’t help her case either is other similar characters were done a lot better. she’s essentially the worst qualities of both sunset shimmer and moondancer cobbled into one. sunset shimmer had a weak transition from villain to “reformed” but her having to earn everyone’s trust and friendship and prove she really was good now was done very well. moondancer had the same weak “lost a friend boo hoo” backstory but her characterization was done much better. she wasn’t evil, or even a bad pony: just anti-social and angry with others. that’s a much more sympathetic and believable outcome ton “loosing a friend” than “i’m a world-destroying monster now hear me roar”.
also not helping is how she was a brilliant villain. probably the best the show has produced in terms of depth, motive, etc. a lot of fans simply hated to see that replaced with (let’s be honest here) basically just sunset shimmer with a combover. she’s also a villain who was already much more likely to reform, being an extremist who’s methods were evil but possibly had altruistic goals rather than just “imma darken/chaos/devour/destroy all the ponies because we need a villain for 44 minutes” and they ignored that in favor of giving her a very cheap “i’m evil because i got dumped boo hoo hoo).
finally, is they are severely flubbing how they’ve integrated her as a character. she’s entirely absent in episodes that don’t center around her, and the episodes she is in have characters dumbed down, acting out of character, weakened, shoved aside, and/or painted in a negative light in order to shill starlight as a character. they’ve never let her just be a character alongside other characters. they’ve never given her character-based humor and interactions alongside the cast while they do their things.
all in all, if you’re able to buy her backstory (or see it as reasonable), her characterization, and how she’s given the spotlight in every appearance, then she’s easy to like. if not, she’s easy to hate. now these are just all my opinions cobbled together alongside observations i’ve made. i’m not trying to pass this as fact or change minds or anything, just give what i at least think is an accurate answer to op.