> Both are well-made romance historical melodramas made 10 years apart
> Has a strong female lead that saves her male lead a couple of times
> Amazing performances from both leads to the supporting casts, and even a senior actor with a prominent role (Suyang in Princess Man and King Yeongjo in Red Sleeve)
> There are a lot of other historical romance melodramas (you can see from the other recommendations here), but these two dramas are both well made, received high ratings, and great reviews in Korea and abroad. Princess Man won best director and was nominated for other awards for Baeksang years ago, there’s a high chance the same will happen for Red Sleeve.
> Both female leads were called historical drama queens after their respective dramas aired
> The leads in both dramas received top excellence awards and best couple awards in their dramas' respective stations at the year end awards for their performances.

Both dramas are set during the reign of King Gojong. This means that the drama is set during a time when there is such a great transitional change going on in Korea (late 1800s). Korea, a kingdom known for being against the influence of foreigners (except maybe China or Japan) is shown to starting up to open to Western influences in both dramas, thus we see the lead characters use the gun more instead of the traditional swords (though some characters still use swords). We also see how Western influence is impacting the main characters. Example is how both female leads in both dramas got fascinated by the western objects they encounter in the show. We also see some men cutting their traditional long hair to fit to a shorter western hair, plus they also trade their hanboks to western suits. Big difference in setting is that Gunman in Joseon was showrn during Gojong's earlier reign while Mr Sunshine was during his later reign.
The character of Lee Joon Gi in Gunman also has similarities with both the leads in Mr Sunshine. LJG character and Lee Byung Hun's Mr Sunshine character are similar in that they suffered a lot in Joseon before they left for another country. Using an identity from another country (LJG using a fake Japanese identity and LBH becoming a US Soldier captain as US Citizen) and wearing Western clothes, their return to Joseon will lead them to more hardships to overcome before eventually becoming heroes to Joseon people. LJG character also has similarities to Kim Tae Ri character in Mr Sunshine. Both parents died, and both became masked vigilantes who do missions which eventually helped Joseon.
Basically, both dramas are about how people lived, survived, and even become heroes of Joseon in a time of impending change

> There are many crossdressing dramas, but what these two have in common is that the female lead lives as a man since a terrible event that occured in her childhood. She disguises as a man for so long that her identity has been as a man not only to others but maybe also to herself that she really got a man's mannerisms
> A love triangle existing between the girl pretending to be a man, her tutor/teacher, and another beautiful young woman (the difference is that the female lead in Painter of the Wind has feelings for BOTH her teacher and the beautiful woman).
>TRIVIA: Actor Bae Soo Bin is in both dramas and he's very important in both dramas. He's the King in Painter of the Wind who gives a mission to the two leads there while in King's Affection, he's the male lead's father whose allies are the main villains (not so sure if he'll stay a villain 'til the end).

=> Both are retellings of the love story of King Jeongjo and his beloved concubine Royal Noble Consort Uibin Sung (her real name is Deok Im but she's called Song Yeon in Yi San).
=> The court lady is shown to have a special talent (painter in Yisan, storyteller and writer in Red Sleeve).
In my opinion, Yi San should be the top recommendation for Red Sleeve fans, come on people, they're both MBC dramas about the story of one of Joseon's best kings and his beloved concubine.

=> The female lead uses her brother's identity to pretend to be a man (though their reasons are different)
=> The 6 main characters plus the villainous royal relative plus the real brother in King's Affection can be compared to the four main characters plus 2 important additional female character plus villain student plus real brother in Sungkyunkwan:
= King's Affection vs Sungkyunkwan Scandal
= Dami/Yeon Seon/Fake Lee Hwi = Kim Yoon Hee/Fake Kim Yoon Shik --> main female pretending to be a man
= Jung Ji Woon = Lee Seon Joon --> male lead, falls in love with female pretending to be a man
= Lee Hyun = Moon Jae Shin --> second male lead who knows main is a girl for a long time but hides his feelings
* Lee Hyun = Gu Yong Ha --> Lee Hyun of King's Affection can also be compared to Sungkyunkwan Scandal's Gu Yong Ha,
both are among the three male leads but neither is the first male lead nor the warrior/action guy
= Kim Ga On = Gu Yong Ha --> third male lead, neither seems to have serious feelings to the female lead, has an air of
mystery to their characters
* Kim Ga On = Moon Jae Shin --> Kim Ga On of King's Affection can also be compared to Sungkyunkwan Scandal's Moon
Jae Shin because both are the warrior/action guys among the male leads
= Shin So Eun = Ha Hyo Eun --> both are female characters that may seem to have a link/affection to the male lead
= No Ha Kyung = Cho Sun --> both are women that will fall in love with their respective main female leads, thinking they are
men
= Evil royal relative (can't remember the name) = Ha In Soo --> villains that are against the main female leads
= Real Lee Hwi = Real Kim Yoon Shik --> real owners of female leads' identities.

Though both sageuks have different target audiences in mind (they have differences as if you want some smart political talk you should watch Queen Seon Deok rather than Moon Lovers) they have sone similarities:
> lots of male fanservice (hwarangs in Queen Seon Deok, princes in Moon Lovers)
> the female leads love one man first then she turns to love a man with a darker past (plus both men wear black most of the time, I'm talking about Bidam and Wang So, Kim Nam Gil and Lee Joon Gi Yeah!)
>both the second men the female leads love have mothers that are obsesses with power plus those mothers abandoned those sons too
> both evil mothers have other sons they prefer over the son (the men loved by the female leads) they abandoned without realizing that their abandones sons are the smartest and their closest ticket to power

Similarities:
> both sageuk OTPs have great chemistry (lots of OTP moments towards near the end of the drama).
> both couples made so much effort to show how much they love each other and each of them proves how much they love their other half (especially true of the main male lead in Moon Lovers and main female lead in Princess's Man).
> side couples with their own stories (whether happy or sad) that made you care about them.
> lots of tragic events happening which makes or breaks the lead couples
> expect some tragic things happening among family members due to greed by some
> important theme in both dramas: filial piety vs love vs power
Difference:
> Most of the male lead characters in Moon Lovers (the princes) except for Wang So are played by actors in their twenties (when they made the drama), while the male actors in The Princess's Man (the 3 friends whose lives are changed due to events) are played by actors in their thirties (when they made the drama).
> You see a lot of politicking scenes in The Princess's Man while there's not a lot of those in Moon Lovers, more of the political dealings (example: King's dealings with various factions) are merely explained.
> Moon lovers is set in the dawn of Goryeo era while The Princess's Man is set in Joseon.

By the way: The Princess Man > Moon Lovers Scarlet Heart Ryeo for me

=> same male lead as played by Lee Joon Gi
=> Lee Joon Gi's characters are both suspected criminals
=> both dramas have adorable little girls, daughters of the male lead
=> the female love interests (mothers of male lead's daughters) don't know the criminal record of the male leads when they were dating
==> Trivia: both actresses for the love interests (Moon Chae Won in Flower od Evil and Park Ha Sun in Two Weeks) played as second leads in Han Hyo Joo's (Lee Joon Gi's love interest in Iljimae) dramas (Moon Chae Won in Brilliant Legacy/Shining Inheritance and Park Ha Sun in Dong Yi).
=> thriller drama with many plot twists and turns, most episodes keeps audience at edge of their seats
=> backstory romance of male lead and female love interests shown in pasts scenes throughout the drama
=> main difference: female lead in Flower of Evil is the detective investigating the male lead's case; while in Two Weeks, the female love interest has a detective fiance who investigates male lead's case along with a female prosecutor
==> female lead in Flower of Evil for me is like the composite character you get if you combined the female love interest, fiance detective, and female prosecutor from Two Weeks into one character.

Both are historicals where w woman pretends to be a man. There are many historicals where a woman pretends to be a man, but what makes this two shows similar is that the woman started to pretend to be a man after her brother's death (and she takes identity of her brother).

Shows are not similar except that Moon Geun Young is the lead in both shows.

However, I am doing this recommendation since I want more people to watch Painter of the Wind as it is a very underrated drama yet an extremely good drama. To understand how good this drama is, first of all the director is Jang Tae Yoo (who also directed another great drama in Tree with Deep Roots plus My Love from the Star and Lovers of the Red Sky). The direction he did in this drama is really good. Second, lead actress Moon Geun Young (who I noticed Catch the Ghost fans sometimes find annoying) won a Daesang in Painter of the Wind. Watch Painter of the Wind to understand how great her performance is as a woman pretending to be a man. Kim Yoo Jung is Moon Geun Young's child actress too, and her 2021 Lovers of the Red Sky show is a reunion of her and this drama's director (both shows have a female painter as a lead).
Drama is very unique, at first glimpse it might look like a simple age gap romance. But the truth is the female lead here has 3 love interests (an older man, a foster brother her age, and a female gisaeng/entertainer). Two of these relationships are two-sided and not one-sided.

I am recommending Painter of the Wind here because most people might know Moon Geun Young from Catch the Ghost (due to Kim Seon Ho recent popularity).

Not too similar except the fact that Lee Joon Gi is the lead in both dramas and the romance of his character and the female lead are crucial in both dramas.
However, I am recommending Flower of Evil to Moon Lovers fans because Flower of Evil is such an underrated drama and more people need to watch it. I know Lee Joon Gi has many fans from Moon Lovers, so I hope his Moon Lovers fans can watch Flower of Evil. Don't undersestimate the female lead, Moon Chae Won may not be the most popular to today's kdrama audiences but she is an acclaimed actress and she has great chemistry with Lee Joon Gi.
As for Flower of Evil fans, it is good to recommend Moon Lovers since it is indeed one of Lee Joon Gi's most popular roles, it's a good idea to watch it for Flower of Evil fans to understand why Moon Lovers fans hype Lee Joon Gi's role in this show so much. And Lee Joon Gi did a great job in this role too.

Both are historical dramas where the male lead is a monster of sorts, a female lead that sometimes dresses men's clothes, plus the female lead's father sort of paranoid sometimes. Drama plots are not exactly the same but the similarities above plus the way the female leads addresses the male lead as seonbinim (scholar) kinda made me remind the dramas of each other.