I'll try to keep spoilers vague, but I'm going to say right out the gate: halfway through episode 22 and on are a complete disaster. This isn't even a case of "I didn't like the ending" but that the ending is objectively bad. Plenty of terrible things I HATE happened before that point, but this was where the writers realized they didn't know how to resolve their plot. It was extremely lazy writing, which I admit shows its face throughout the show in some ways (the full dynamic of whatever the hell the Wang family was up to with the 2nd Prince, for example, was never really explained). My big beef with this is that I really don't understand how the FL can be so extremely clever and strategic only to suddenly become stupid and careless.

A large part of why the ending is so terrible is because everything leading up to it was so GOOD. This is one of the most entertaining C-dramas I've ever watched. I LOVED how the FL was portrayed up until the very end where she became a dumbass who suddenly couldn't grasp any situation she was in (even though she's spent her entire life being hyper-vigilant).
I also don't know why they decided to add in pointless tragedies? None of the people who died at the end were this stupid. The deaths before episode 22 were also unwanted but they at least served a purpose to the story. The others didn't do anything but summon another LOUD round of one of the show's only two songs.

All this said, I will probably watch the show again at another time. Next time, I'll just stop before it goes downhill. I should talk a bit about the perks.

- The Characters: There are so many good characters, sweet ones and stupid ones and kind ones. While they aren't all super complex, they're almost all quite loveable or sympathetic. Second male lead syndrome is a bit painful in this one.

- The Flirting: Constant. It's fantastic, sweet, and hilarious to watch everybody flirt.

- (Some) Acting: Some acting in the show isn't SUPER great but the really important scenes are beautifully done. The lead actress in particular is really incredible and melding with her character. The ML's face is usually hard to read unless he's comfortable in the scene which I think is very endearing (I love scary faces worn by people who are super sweet and doting).

If you like this show, I would recommend My Uncanny Destiny for a semi-similar plot with a lot more satisfaction. I definitely feel like watching that after watching this. These shows' endings are like night and day.