This was my second ever kdrama; it pulled me into the world of dramas, and I've been hooked since then.
Do not listen to the mixed reviews; take it from someone who has seen a ton of fantasy dramas (around 45); this is one of the best.

This isn't a review of sorts; I don't remember the scenes well enough to do so.
But I recall the stellar acting and plot. You'll love it if you appreciate fantasy, romance, mystery, drama, and a sci-fi parallel worlds scenario. Give this drama some time; don't drop it after the first two episodes.

(I was obsessed after the first episode, but I know how different people can be; if you have any second thoughts, take my word and watch it.)