So basically episode 2 - 15 is filler.

How did Do-Jun have knowledge of the future? Why didn't the future change? Why didn't he prepare for the death like he prepared for everything else? Why didn't Do-Jun help his poor family when he had enough money to do so? Surely after nearly dying with has Grand Father he would be smart enough to have better security. But also, how did Hyun-woo record the phone call in like 2005? Why didn't the manager just hang up the phone after talking to Hyun-woo?

Is it worth watching 15 good episodes just to be extremely disappointed and dissatisfied with a horrible ending? Maybe. But it will leave you questioning if it was worth it.

Many plot holes. Story should have gone the same way as the novel. It was still entertaining but it could have been A LOT better. Ending ruined it for me in my opinion.