In both dramas, FL and ML go down to the mortal world for tribulations. While it happens 7 times in LYST, it happens once in Ashes of Love. However, their story also spans a few lifetimes, so it's a bit similar.

The lead couple body swap from time to time and its fun when do.
What's more the actors in both dramas also do a wonderful job enacting this body swap.

In Perfect Marriage Revenge the guy is emotionally cheating (married the FL to be near her sister), in Marry My Husband the guy is straight out cheating, the FL finds them in bed together.

In both dramas, female lead go back in time, in Perfect Marriage Revenge the time is much less, Marry My Husband provides the FL with more time.

While both FL's are out for revenge, the story differs in how they both go about it.

In both dramas, male leads are green flags that go out of their way to look out for the Female leads. Both male lead also go back in time however aren't aware the the female lead did as well at least not for a while.

Both shows have a perfect casting, so the acting is also good.

While Welcome to Samdal-ri is sweeter, Our Beloved Summer gives the same vibes.
The males characters in both shows are adorable and heartwarming.
The female characters in both shows are no-nonsense career women.
Both are second chance romances.
ML and FL in Our beloved summer bicker a bit more than Samdal and young pil.
These two are perfect examples of romcoms.