This drama is really intense and intriguing ! After every episode you will wonder what is going to happen next!
It is true that there is this 'call from the future' part similar to the drama Signal . If you have watched Signal and liked it, you might like this as well. I find this drama even more intense and fast paced than Signal.

The lower ratings don't do justice for real. For anyone who is seeking a a romcom or romance between the leads may be disappointed. However the leads have a good chemistry and we don't know yet if there will be sparks in the future. XD ( I would love that)
I binged watched 8 episodes ( i don't usually binge watch like that these days, but it was hard to stop) then I had to wait for the 9th episode---IT WAS HARD TO WAIT!

Give this is a shot if you like intense dramas or thrillers, you will love it.