Voice 2 (2018)

Both dramas are thriller mysteries that will keep you hooked on the storyline from the start. I'll let you judge the rest, but if you enjoy one, you’ll likely enjoy the other as well.
Including [Voice Season 3]

This is the next chapter to the the 1 season. The main detective can hear things that no one else can so more cases to solve.

well, so many people have given out recommendations and i am surprised that no one is yet to recommend Voice season 2 and 3 when the male lead character there is so similar to the one in Flower of Evil. in fact Voice series are OCN dramas so they are meant to be a lot darker and with less emphasis on romance which could be a plus for a genre like this. there is a good reason why the Voice series keep getting season's extension, you gotta watch it to know. enjoy!

Both shows pit the ML against a cult:
>> In SM2 the ML is trying to save/help his townsmen from a religious group who are really aiming to take away their money.
>> In Voice 2, both the ML and the FL discover and try to take down a cult/group of serial killers.

Both shows pit the ML against a cult:
>> In SM the ML is trying to destroy a religious cult and save one of his classmates (the FL).
>> In Voice 2, both the ML and the FL discover and try to take down a cult/group of serial killers.

If you loved Park Hae Jin 's psychopathic character in this, definitely watch Voice season 2 and 3 for its spectacular performance by Lee Jin Wook. Voice 2 and 3 did an amazing job at fleshing out character like this that progressively worsen because of evil, manipulative forces around them. Enjoy!

-episodic cases
-a core story
-revenge based plots
-morally grey main leads
-no romance// but a lot of tension teamwork and chemistry
-good team
-badass leads
-really dark storylines
-blood gore and action
-taxi driver explores giving justice outside of the legal framework, whereas voice is very much pro-police (except out guy kangwoo love him sm)
-voice has a more personal and dark storyline than each of the characters in taxi driver, idk I feel more connected to voice characters
-both are thrilling, voice is more focused on uncovering a mystery whereas taxi driver focuses on bringing justice to the wronged, it's less mysterious
-amazing action thrillers both of them, keep you on the edge of your seats!