First of all, I really enjoy series with this sort of theme. I love folklore and supernaturall stuff and add in a little religion flavouring. I just find those themes really interesting so I sort of knew after finding out what this was about that I would enjoy it. Had fun fighting scenes, some actual scary bits (those ghost kids man), fun characters (I love that the gateway to the afterlife is just looked after by some middle-aged couple).

Pros:
The Foxes: All of the foxes are the reason to watch this show. That might seem like an obvious statement given the name of the show but honestly, if there were no human main characters and just immortal beings trying to save the world, I think it still could have worked. Perhaps even worked better.
The Other Immortals: I loved Granny. I loved her husband. I loved all the other immortals that Lee Yeon encounters. Even the baddies.
The Theme: A world where immortal/supernatural beings live among humans. Always fun.
THE FOX BROTHERS: I will be talking about this later.

Cons:
The Main Love Story: Felt forced. I LIKED Ji ah. I found her interesting and a fun character but I felt like the chemistry between her and Lee Yeon was just off. I don't think it's the actors, I just think they're written in a way that seems to have less depth and impact than the other bonds we see in the show.
Those Sneakers!: I liked most of the stuff about this show but those sneakers. No. Just no.
Ji Ah's Parents Story: I get why it's in the story, kind of but I think it feels a little bit...oddly placed within the story and her parents just kinda being chill about having been missing for so long seems odd to me.
The Food: I'm only kind of kidding. I was constantly hungry watching this series. Had to make tteokbokki a couple times.

But let us return to the Fox Brothers. At the end, Lee Rang makes the joke that the piece Ji Ah's making should be called the Tale of the Nine-Tailed Brothers. Thing is? It should be. The main romantic story in this series is fine but the real EMOTIONAL story is the story between Lee Rang and Lee Yeon. I get that a romance based series is going to appeal to people more easily than a show just about the emotional heartache, betrayal and eventual love and sacrifice between two brothers but honestly, I wish the whole thing was just about their brotherly love and the foxes and immortals around them that they care for. Although I tried really hard to be invested in the romantic story between Lee Yeon and Nam Ji Ah, I just didn't feel it. However the brothers interaction was always good. When they were fighting and enemies, when you learn about Lee Rang's tragic issues surrounding his brother, I got CHILLS when the brothers first worked together and I was BAWLING at the end with the video messages. The series is worth watching just for their story alone.

All in all, this is a great series with some really fun themes (folklore, supernatural beings etc) and a really heartwrenching and beautiful story about two brothers.

Also there is a romance that happens in it.