For those going into this show who aren't used to over the top situations accompanied by over the top acting, I'll give you the fair warning that this show contains a load of all that.

Lets begin with the acting, and how it ties in with the character portrayal:
Pros:
The actors and actresses themselves execute their roles perfectly. They each have distinct mannerisms that really bring the characters to life. They embody whatever evilness, smugness, or good-ness their character brings to the show without revealing all intentions; yet they still help the viewers to understand that nature of said character. It leaves room for the us to make deductions about each character, and in that sense, I thank the directors for not treating the viewers like idiots.

The best examples of this would be Cheon Seo Jin, played by Kim So-Yeon, and Shim Suryeon, played by Lee Ji-ah. Seo jin herself is a damaged woman who grew up in what most would call a toxic family, and her actions and over the top-ness are understandable in that sense. Kim So-Yeon clearly understood that this character would act irrationally, overtaken by her emotions most of the time, and that is how she portrayed it. As for Lee Ji-ah, her character Shim Suryeon was a force to be reckoned with the whole way through the season. She held her character's composure, and knew when to put on a different front as if she was acting a whole other character.

Cons:
Definitely the over-the-top-ness of it all.
The directors HAD to be intentionally making the characters act way over the top. To be quite honest, I'd only recommend this show to those who can tolerate and don't mind this type of acting.
I was alright with it because I expected this sort of acting already judging by the kdrama scenes I've seen through the shows my mom used to watch, but its definitely not for everybody.

Music:
Ill keep it short and sweet. This is a kdrama that revolves around opera and classical music, of course the music is gonna slap.
Admittedly, some of the soundtrack can get repetitive, but eventually it just becomes a signature thing that gets you a bit hyped. There ARE a few moments though where electric synth would come in or something like that, and you could only think "What were they thinking with this music choice", but overall, its filled with some absolute classical bangers.

Characters:
There's just so much to say....
Pros:
It begins on an exciting note that sadly dials down after that first scene, but it gives you time to get a grasp of each character,, along with their roles, social status, pasts, and relationships.
This is a character driven story for sure, so by understanding why each character makes the decisions they do, it only helps to expand them. It leaves the viewers wanting more from what they've seen. The viewer wants to see how each person will develop, and you will find yourself rooting for at least one person for sure.
These characters you grow to understand more are what keep you hooked in the story as they are pushing the the plot.
You will find yourself rooting for at least one person, and will be constantly impressed by how certain character plots develop.

Cons:
Some characters are left with nothing, just given a brief backstory so the viewer can go, "Alright. Fair enough," but the directors seem to refuse to elaborate on any of those things. Sure, they might bring it back later, but why show it now? Especially at such a time where other much more important things are going on?
There are also times where someone acts completely out of character, and you're forced to just overlook that moment since it makes no sense with the story. It just feels like an afterthought to make a character seem more 3-dimensional.

One of the things that bothered me most was that the kid we're supposed to care about the most, Bae Rona, was just so.... uninteresting and unlikeable. She couldn't communicate at all despite what they show earlier of her being witty. She is also shown as kind and generous, but she comes off as bratty, and her (supposed to be) strong willed mom lets her Rona walk all over her. I'd rather much see the progression of a complex and consistent character such as Seojin's child, Eun Byeol.
The worst part of all in the character writing, was that they always had chances to develop a character, and they just WOULDN'T.

Finally, Plot:
Its messy and the execution is, dare I say, bad.
It feels like a story where the writers had so many good ideas. Ideas that didn't flow, but they decided to write it in anyways. It's enough to keep you engaged and enraged, but so so messy.
Sometimes, events that happen just feel like they never happened. They jump from plotline to plotline so quickly, that its hard to see where everything ties in, and you're just left hoping that they bring something back up since it makes no sense to overlook it.

Final Remarks:
If you're somebody who deeply cares for story and character development, this show isn't for you.
But if you just want a good time, hell yeah, that's why I stuck around. Its not a show meant to be hyper analyzed, even if the directors intend it to, because if you hyper analyze it (like I just did), there are way too many flaws to count.
It can leave you ooing and ahhing, and honestly, its feels like a guilty pleasure the whole way through.
I wouldn't normally recommend a show this objectively bad, but if you just wanna turn your brain off and/or be entertained, watch it.