Both original novels of these two series carry quite realistic, dark and gory undertones. Like it would depict deaths, murders and corpses in a shuddering, gruesome manner (for both bad guys and good guys alike). They censored and tone down this aspect of the story when they adapted them into TV dramas, but they still try to show/hint at the darkness in the characters and story.

Both series were very closely adapted from their novel version, so I believe this is one of the many reasons why they became such a hit.

The difference is one is bromance/boys' love while the other is romance. One is wuxia and the other is not.

The story is not exactly similar and its a modern drama but the Main couple have similar personalities.

Ling BuYi for some reason reminds me of Ou Chen with his overbearing/controlling methods and making decisions for the FL for her own good. Also his deep almost obsessive love for the FL to the point where he can't live without her and he made sacrifices behind the scene to make her happy.

Chen ShaoShang is also kinda similar to Yin XiaMo, savage, practical and scheming, doesn't consider love as priority as long as she can live a stable life. Treated ML coldly knowing he loves her, at first.

Both care about their loved ones and are vengeful. Both develop throughout the story and learn how to truly love.

Theres 2 adaptations of Summer's Desire, and I think both are worth watching depending on which pair actor/actress you like better.

Same supernatural concept with different side stories between human and spirits.
Male Leads are immortal.

Supernatural/fantasy element during republican era.
Both have male lead that had lived for a long time (immortal). They also tried to help others and vanquish evil spirits.

Queen Lau reminds me of this old drama My Bratty Princess.

Both FL is funny and totally change the atmosphere of the palace once they entered.
Another thing is they're sassy and not easily bullied. They know how to fight back.
Both FL is the daughter of a high-grade official in the court.
Both assist the emperors and give them a whole new perspective on how to govern the country.

Both have supernatural elements set in the Republican Era.
Both are episodic as in main leads encounter many other stories of humans and spirits before eventually leading them to the finale of their own.
Some of main leads' pasts are shrouded in mystery.
Both have a romance that spans over a thousand years.

-Same concept. Twin Sisters identity swap.
-Younger sister assume the identity of talented older sister while older sister mysteriously goes missing.
-Younger sister fell in love with ML

Both are set in China Republican era, the Sino-Japanese war. Stories that focus on the relationships surrounding a prominent family during the time. Both have obsessive/stubborn main leads and love triangles.

Both are set in China Republica Era. Both have an angsty love story about love and betrayal. They also have misunderstandings between the main (married) couple.