(I'm going to do my best not to write spoilers)
For me this was a super good kdrama so where should I start?

In the beginning the drama really takes you along with its feelings. probably the cinematography did the story so well that you really feel the feelings.

Second.
People behave strangely when they hear a clock ticking and become deeply afraid.
You can see that in all the "reboots" that the drama requires. It is quite understandable that this becomes boring for some people. but to me it made perfect sense. I don't want to spoil it, but if you've watched it, you can see these stages clearly.

The third layer. Myul Mang and Dong Kyung's journeys to living a fulfilled life. They are both depressed and wish the world could just end so they would never have to suffer again.
Both felt lonely and out of place.
One had to learn to love even when faced with the inevitable end, and the other had to be selfish even when faced with the inevitable end.

the fourth layer for me was the religious aspects, of having two gods, one the creator, one the destroyer, and both were created by and for man to explain the randomness of suffering. This is part of many religions. But Buddhism especially has had to endure the ethos of the same suffering in different ways until you accept the fate and learn the lesson in this life and grow. Here too the frequent repetition of their old patterns is explained. Especially the part in the middle where they can both see what they would have been if they hadn't grown together through their pain and their joy.
this drama was really a great drama
but I didn't like it that much because this drama made me cry a lot.

By the way, I these OSTs of this drama were really good. Normally I'm not a fan of that