This is my first review for a drama. I'll try to explain my point of view without too much spoiler.

I've seen a lot of drama and film about time travel, and they all follow certain rules. Here all the principale rules are respected like the temporal paradox (the biggest one) ...

Not following certain rules is not disturbing, but all problems in this drama are on the little details (Like why Seo Hae take the time to sleep when she want to save her father ? Why she's going through a wall for no apparent reason ? How did taesul take the time to build a bunker in 12 hours? Why when sigma is in his workshop we can see the light on his windows, and when he go outside it's the nuclear night ? Do you really think we survive a sandstorm just with a bandana? ) It's these little details that make the drama's credibility not great.