MRIAG isn't out yet but some of the story seems similar to MGIAG. Only in MGIAG the ML has the females pearl and the FL wants to become human.

These dramas left me with the same feelings. They are quite different but both have one character keeping secrets from the other character and a similar marriage arrangement/relationship progression.

I think they have a similar vibe. DISCLAIMER I am only up to ep 31 on First love.
PYHOMS is more focused on the romance of the main couple than in First love and has lots more Awww moments. The romance in First love is slower moving and a little more "innocent".
Both have;
Long distant relationship/breakup (SPOILER;which I did not like in First love)
No real bad guy characters.
Characters stay true to eachother.
Smart ML willing to do almost anything for their girl.

More time spent on the main leads relationships with friends and family in First love.
PYHOMS starts at university and continues on to worklife for some characters while First love starts in high school and continues into university life.
I like the stories of the secondary characters in first love better than in PYHOMS.