Overall: this is a condensed version of the series which was 12 episodes about 40 minutes each = 480 minutes. The movie version is 125 minutes long and I liked it more than the series version because it cut out boring side couple stuff and stuck with the focus of Ai and Nhai. You can read my full review of the series here https://mydramalist.com/profile/blcompilations/reviews/233757/ I'm going to point out some differences.

What I Liked
- left out the cute rooftop/coupon scene and there might have been other cute scenes they left out as well
- better ending with the stargazing instead of that random store/shoe tying scene
- had transitions between scenes to help make it feel more cohesive/time had passed (though it can feel a bit choppy)

Room For Improvement: if I had edited this I would have changed a few additional things and then I would have rated it an 8.5
- in the flashback (which I would have shortened) cut out the dads being awful to Ai, the dads lied to him and he has a right to be angry/confused
- added back some of their cute scenes