Best thing:
The drama managed to focus on romance whilst recognizing that romance is just one part of the character's lives. It's such a simple thing that they did so right. It's seriously such a rare quality as in many romance saeguk: they either show too much beside romance just to show off the character's virtues; or make the characters seems like crazy people who only live to love (UGH the countless lovestruck emperors and runaway princesses wagering their country for love).

Another great thing is how the female lead helped the male lead A LOT. I like this situation much better than the protagonist being the debtor, which is more often the case.

Nope:
If it weren't for the icky court lady cult plot(???) this would have scored higher. Yet that part was so nonsensical and forgettable and long that if it weren't for how good the OTP is, this would have scored so much lower. They could have gone a thousand other ways with the court lady thing, yet they chose such a nonsensical way. It's not weird because it's a cult, I'm saying that this particular cult is so damn ?????

The rewatch value is especially high with this one, there's the feel good aspect and the skip button. Another note, this drama reminded me so much of Moon Embracing The Sun. I'd have to say Red Sleeve is the better one between the two still.