When I started watching, I wasn't exactly a fan of the pairing but they both grew on me. I enjoyed some of their interactions, some were far too silly which again points to poor writing. In the hands of a good writer, this drama could have done a much better job.

The time travel element wasn't ever fully explained.
Why did it happen?
Who sent her the message?
What happened when she back?

What spoils the story is that they went so far to create a clear distinction between Lin Miao and Lin Wei Jun, so much so that it is very difficult to reconcile that they are one person. The ending is so rushed and ambiguous that the viewers are left to figure out what happened.

The simplest explanation should be: Lin Miao went back to her time 10 years in the future, during these 10 years Lin Wei Jun grew into herself becoming Lin Miao and that was who came back for Jiao Yang who waited for her.

But then so many new questions arise. Since Lin Wei Jun life was altered by her future self and Jiao Yang, wouldn't her future self have new memories? Would she be the same Lin Miao that visited the past? Or would she be more like her past self? And what does that mean for their relationship?