Recommendations

The main actor :D
And of course - good plot, actions scenes and romance :D

Consists of similar comedy styles between the two dramas and bickering otp becoming lovers storyline.

the background and tone are completely different. so you may be surprised at my rec.
i don't what it is but i think both dramas share the inrigue and quality that i look for

tho this has a different plot it shows beautiful cinematography of mountains and trees too + great character development....also the chemistry between shun and yakusho is like the chemistry between sometani and hideaki. To oguri shun fans this is IMO his best performance so watch it LOL.

Both are action dramas, Fast paced, and really interesting.
Top this up with great actors and mysterious bonds between them from when they were kids and because of their parents and here you go. They're just GREAT dramas.

They both are pretty cruel dramas. Both are made by the same channel, OCN. Both have these special teams solving the cruelest crimes. I really recommend both ones

Both are cute, light hearted dramas about a small business that helps its customers. Both dramas have got supernatural elements in them.

Both are action based drama, where the main character is doing a lot of fighting. The female lead is the same actress in both dramas. Both dramas involve a secret to be discovered and slowly seeing the connections between people. The two dramas give off the same vibe.

Both are revenge dramas, and both deal with very mature subject matter. Qoa, death of a child, missing you deals with rape and other really touchy issues.

Just because you'll fall in love with Jin Chang Wook. Even though the two stories do not have any similarities you'll definitely fall in love with JCW. <3 <3

Both have aliens living in Earth due to unexpected circumstances and hilariously trying to adapt.

In both the movies, the husband is scheming behind his wife's back.

I watched secret first and it's one of my favorite revenge dramas, but I have never seen such a blood boiling drama in all my life as QOA.

Gong HyoJin's amazing acting takes on a different, and slightly less 'intelligent' role in The Master's Sun - but pulls it off as flawlessly as she did her eccentric and complex character in It's OK, That's Love.
Both dramas have a lead character (Joong Won in The Master's Sun, Hae Soo in It's OK, That's Love) that sees themselves as a little bit superior and doesn't want to have much to do with the second lead initially, but turns into a comedic and cheeky relationship.
Both have psychological elements to them which can be very sad. Without giving too much away, a departing of a certain soul in TMS reminded me of a soul the metaphorically leaves in IOTL). They also deal with healing wounds and fixing problems of the past.
Both are funny and feel-good dramas.
TMS is a little more slow-paced but has a more complex plot; IOTL has more side-plots, a less complex main story but is more high-intensity and high-emotion.

These are both movies that can be easily recommended without giving another movie as an example, but both of these movies have similar themes. The biggest of which is probably injustice - the 'baddie' in the end, wins. The next biggest is family. The strong Father-Daughter relationship in both of these movies is touching and heart-wrenching at the same time. They both also a feel-good, but very sad movies. If you like one, I have no doubt the other would be to your taste.