=> Both Hyun Bin dramas that are romance comedies where he has sizzling romance with the female leads
=> Hyun Bin's parents want him to marry someone else in both dramas
=> The female lead actresses in both dramas are two of the most successful actresses in Kdramaland , both having won Baeksang awards in both dramas and films, so good acting is indeed guaranteed in both shows
=> Both dramas were extremely popular after airing, to the point where Hyun Bin was shipped so hard to both female leads immediately after both dramas aired
Interesting Trivia about the two female leads connected to the two dramas:
1. Ha Ji Won (Secret Garden female lead) also played a North Korean person in love with a South Korean like Hyun Bin, in her drama King 2 Hearts
2. Son Ye Jin has a cameo in the last episode of Secret Garden

=> A romance feauturing a special forces captain and a woman with her own accomplishments in her chosen profession.
=> First episode shows male lead fighting another soldier
=> Also features a second couple (the romances of the second couples have a bit more pain than the leads)
=>The second female lead and male lead are not in love with each other, but their parents want them to marry each other
=> Male lead often protects the female lead
=> Both male leads have their own team of soldiers. This is natural since both male leads are captains. Some of the people on these teams got close to the female lead.
=> Some parts of both dramas are set shot outside the Korean peninsula which gives a lot of beautiful scenery shots (Greece representing fictional country of Uruk for DOTS vs Switzerland for CLOY).
=> Both dramas feature North Korea (this is obvious for CLOY, but the male lead in DOTS also did have some missions in North Korea)
=> Both dramas are big hits and extremely popular when aired
Interesting Trivia (please don't hate me for adding this, I don't mean any harm):
=> The lead couples in both dramas are (or at least was in DOTS) both real couples that got married . (DOTS couple did divorce, hope the same won't happen to CLOY couple)
=> Female lead in DOTS and male lead in CLOY dated each other many years ago, their drama in 2008 is called World's Within

=> Same writers and probably same creative team too.
=> Both heavy on politics, might bore some people but if you're really invested, the dramas are both really satisfying
=> some supporting actors appear in both dramas (ex: Hong In Bang in 6fd is Seolwin/Mishil's lover in Queen Seon Deok + Alcheon in Queen Seon Deok is Bangwon's eldest brother in 6fd)
=> many memorable characters from main characters to supporting ones
=>great warriors/ swordfighters are depicted in both dramas

=> Both are Kim Tae Ri dramas
=> Fencing is featured in both dramas
=> The coach in Twenty Five Twenty One is also in Mr Sunshine as the mother of one of the female lead's suitors
=> I'm particularly using this comparison for Twenty Five Twenty One fans to watch Mr Sunshine as Mr Sunshine is underrated among international fans and new Kim Tae Ri fans should check it out.
=

This may be weird, but I think the two shows have a few similarities. Both have some comedy to keep the audience entertained. Both shows' characters (or at least some characters in Vincenzo) also obsessed about looking for gold/treasure.

=> about a person who looks like the supposed real king/crown prince, the person was suddenly put in the high position of king/crown prince
=> the person that wasn't supposed to be king/crown prince proved himself/herself to be a good king/crown prince while he/she is on that position
=> the real supposed king/crown prince has a half brother, some of the plot revolves on the mother of that brother plotting against the crown prince/king (without her knowing that the crown prince/king is not the real one)
=> the main villain is an old official audiences will love to hate
=> BONUS: both lead characters (plus lead female in The Crowned Clown) in both dramas are played by former child actors with lots of acting experience so we can expect great acting from them

Lee Se Young plays a royal loved by a king in both dramas. Both Yeo Jin Goo and Lee Jun Ho are among the best actors playing Joseon kings.

> Both dramas by writer Kim Eun Sook. I'm recommending two shows she did, both of which are of soldiers, but the feeling of the two dramas are quite opposite. DOTS is romcom and Mr Sunshine is more melo.
> Both lead males are soldiers.
> The male lead in DOTS and the female lead in Mr Sunshine are both characters fiercely determined to protect their country
> The second lead couple' actors in DOTS appeared in Mr Sunshine as parents of the female lead.

Arthdal Part 1 is the first if the three parts released (all of which are Arthdal Season 1) while Arthdal Part 3 is the third part. There is also Arthdal Part 2, which must be watched between Arthdal Parts 1 and 3.

Arthdal Part 3 is the sequel of Arthdal 2. There is also Arthdal 1, the beginning part. But all these Arthdal Parts 1-3 are all part of Arthdal Chronicles Season 1.

Arthdal Part 1 is the prequel of Arthdal 2. There is also Arthdal 3, the third part. But all these Arthdal Parts 1-3 are all part of Arthdal Chronicles Season 1.

Both dramas are about the rise of Lee Bang Won. Difference is King of Tears is meant to be a more historical take while 6 Flying Dragons adds some interesting characters.