I had seen so many people mentioning how good this drama was that I decided to give it a go having nothing else to watch. I was disappointed and I didn't even have high hopes as I find hyped shows are usually not my cup of tea.

The first third of this drama was hard to watch and I had to push myself to continue, mostly I found the portrayal of a 19 year old girl very unrealistic, she was very childish. Maybe it's just me, but I've never met (nor was I that way) anyone that age to act like that. Then I kind of got used to it by the middle, but also she seemed to slowly get out of it when she turned 20, what was also unrealistic. To top it over, Goblin was doing the opposite and as the drama goes he becomes more childish. Not going to lie it was funny at times, but overall it was mostly cringy.
The age gap of the characters was problematic (without taking into account the 900 years) and to me it made it worse the fact they blatantly tried to make this look better by making him more childish, also because it felt it tainted his character as this important and powerful Goryeo warrior. I feel there was a problem with trying to keep this balance of wanting to be serious and sad and tragic with the romcom aspect, I couldn't take things as seriously.
I think the story would have been a lot better had they started it when she was 29, it could have been way more mature. I did like the relationship of the 3 as housemates though and I found it the best part of the show.

There are too many plotholes and I could give it a pass if it wasn't because they had plenty of running time to address them. For example, the images of their Goryeo lives were repeated over and over way too much but in the end I didn't feel they fully showed well enough how things happened. Despite those images, I'm being told what happened more than shown, what is a shame. A lot of times the show seemed to go in circles not wanting to commit to a path for the story, at least not until the later episodes as usual (I seriously dislike this common thing of not doing anything until two episodes of the end, make a film instead!!), but by the end I was already kind of tired of the story to the point that I couldn't care enough for the consequences that were about to happen to the characters. Talking about characters, so many side characters with lost potential and so many plotholes in all characters.

The ending is... I don't want to say bad because it could have been worse, but... it's bad. Could have been poetic, could have been satisfactory but it's none and it's solved in the most weird, anticlimatic and pointless way in my opinion. So much potential for epic-ness wasted in there.

I have watched worse dramas than this one, but I still don't think I would be able to recommend this one if simply for the fact it's too long and not much happens to justify its run time. If it's because any or all of the actors, then go ahead, but if you don't care about the actors and are there for the story then I would say look somewhere else because this is not it.