Train is an excellent drama that I've described to friends as "What Christopher Nolan Thinks He's Making". It's twisty turny and the way that it plays with alternate universes and the idea of fate is really interesting.

I'm currently in the middle of a rewatch of Train with my dad, who has never seen it before. He is confused, but getting more animated as we go and is now at the point where he tells the people in the drama that they're being dumb, so I assume he likes it. For me, the rewatch is interesting because I'm able to pick up on things that I didn't in the first watch through.

Spoilers after this!
I'm sure the way that it ends isn't for everyone, but the idea that moving between the universes is what causes the same things to happen again made me go ? the first time I watched it. It's a deeply tragic concept and Do Wan leaving to protect Seo Kyung only for her to chase after him....It is everything that I love.