The story kept me interested enough to binge-watch it in 3 days.

But, too much plot armor; characters (especially FL) making illogical decisions too many times just for the convenience of the story to make MC being a hero saving the day all the time.

Also, the realization hitting the FL (from 2nd world) about ML was too plain and underwhelming (compare this point to "welcome to life" where it was done pretty good if not excellently).

The lack of chemistry between the 2 leads was quite apparent. Also, it could be just me, but, I found ML's acting to be over-the-top, I mean all he's doing the majority of the time is making an ugly-crying face while clenching his jaw, that's it, that is his whole intense acting, but still not too bad or out of place, but it was too much doing the same expression all the time.

Still, a must-watch. Although it is lacking the emotional connection you feel to the story/characters, such as rooting for ML or whenever any bad thing happens to ML or FL, then you feel sad - yeah, I was watching such moments in passing - like let the story flow however it is, doesn't matter or affect me (maybe it is too cringey, but still, I like those shows the best where if anything happens to ML or FL, I cheer/feel-sad with/for the character).

A spin-off with multiple (~4-5) worlds would be awesome.

Also, Soo Jin was beautiful as always.

PS Read this interesting comment by user Maika, making almost all the interesting points/plot holes I wanted to make. - https://mydramalist.com/52351-train#comment-6717695