Recommendations

Female lead is not only the same actress, but the characters are suuuuuuper similar! Cheerful, optimistic, etc etc.

Supporting female is also similar: Rude and obnoxious model/actress who become likable.

Main leads have met before, male lead does something nice/significant but only the female lead remembers/knows.

So I don't give away any spoilers I'll be as vague as possible:

The feuding male characters are similar in both dramas.

Male lead has a hot temper, is controlling and he has a jealousy issue.

There are probably more but I'll leave them alone =)

Almost the same story line, normal girl meets and does something significant for her boss. She asks for nothing in return which causes her to catch the bosses attention and things proceed from there. There are even identical situations in these dramas. Main differences are the best friend and the female lead has a secret she's hiding from the male lead!

both drama Life and School 2013 are about the bullying in school and true friendship .
if you like school drama you will definitely like them both

Both story take place at the same period of time and deal with resistance against japanese occupation. The relationships develop in a quit similar way. The lead person goes undercover and sacrifice things for the mission.
I felt like Rookie Agent Rouge is a kind of female version of Bridal Mask.

Both have marriage as the end goal. Also Yamapi stars in both :)

Both are fantasy dramas Both have adorable, somewhat mischievous leading ladies.
Both have an element of the couples uncertain future, since they "from two different worlds." One is literally a different world and the other is figuratively, but that fact threatens the happily ever after of both couples.

The leading man, in both dramas, is sought after by many women but he show zero interest in any, until he meets the leading lady, who is like a breath of fresh air. The leading lady, in both dramas, are adorable, energetic, and independent.
The leading man is decisive and is the pursuer. Since the leading men in both are irresistible, the leading ladies fall easily for their good looks and charm.
Even though Love O2O is not a fantasy drama, it does have a fantasy element, with the video game they play. The game element also allows this modern day drama to include a bit of the traditional Chinese clothing and hair styles.
Main differences: Be aware that in The Eternal Love there are some really cheesy special effects.The Eternal Love has a backdrop of Royal politics/Sorcery.
Love O2O has a back drop of social media/College-life/business.

This drama I think is a sequel to Xuan-Yuan Sword: Scar of Sky. I suggest watching Scar of Sky before watching this.

the same time-travel drama because of their first love both have humors in it though Proposal Daisakusen is more of a slice-of-life/love-story drama nonetheless, both stars real-life buddies, Jaejoong in manhole, Yamapi in ProDai.

I don't know why but I feel the same vibes. The main characters are pretty similar, she is a strong one. They are both school dramas, with good romance and bromance

Both this drama and the film Tenshi no Koi deal with an age gap relationship wherein the male is the older lead.

Both deal with disease and illness in characters and both seem to have underlying deeper meanings.

Both are about chasing a serial killer and corrupt higher ups.
Worth watching drama.
Chilling thrilling.

Both are about chasing a serial killer and corrupt higher ups.
Worth watching drama.
Chilling thrilling.