Without much spoilers:
I think this story is one of the best time travel stories I've seen. It is definitely worthwhile and meaningful for such a short drama. The various decisions the two main leads did for each other is truly admirable. The ending was sad but it gives hope to the watcher. Hope that their story will end well.

With more spoilers (how the female lead did what she did was really worth it even though I spoiled it a bit):
The two main leads end up doing so much to save each other and their friend. By the time the female main lead decided to do one last thing for the male main lead, I was really sad. She gave up everything she will experience (and lived through it while knowing what she missed) so that they can have a brighter future. Where their friends will never have to go through all this. Where the male lead she loved dearly won't go through this. The story of the female lead is truly admirable. If there was a part 2 (I doubt), I really hope that the female lead will be able to experience everything she was suppose to (but gave up on to save everyone from the pain).