A deeply flawed yet highly entertaining ride this drama has been.
☆DISCLAIMER☆
This review is only to those who have watched season 1 and season 2.
I will be discussing each aspect of my rating separately.

Story and writing:
The story, in terms of the fantasy and lore, unfortunately suffered a lot this season.
Season 2 hits off with a flash forward 3 years after the end of S1, we are shown quite a lot of clumsily put-together flashbacks to explain to, or rather mystify, the viewer as to what exactly took place after the death of the FL in S1's finale, and even after we manage to satisfy ourselves with the explanation given to us, we are still dealt some comically mystifying and convenienty mashed up rules to the magic involved in order to satisfy the needs of the plot and make it move forward.
To elaborate further;
Much of the rules, if they were ever properly explained didn't make much sense and left one *rolling eyes* mumbling okeeeeey!. We also come accross a couple of contradicting aspects and sudden power shifts like healing powers etc, that in hindsight leaves one wondering why they were never utilized prior. Also seeminly highly wise and powerful characters would constantly be changing their explanation of how the magic behind soul shifting works, and even worse things just ultimately transpire in a totally different manner. other times powerful side characters (park jin, seo yul, master lee) would mysteriously vanish at the most critical moments only to suddenly reappear after sh*t had already hit the fan to stand around and discuss it. A lot of these minor frustrations add up to make one feel like the writers were giving themselves enough viable cards and options to wriggle their way out of any tight spots that come up, all thanks to the highly sophisticated and complicated world that they themselves created in the first place.

Among the other smaller gripes that I had with the story writing, was how everything was built in a way that ensured our main leads were brought together, and despite that being a common trope of many a rom-com plot in K-dramaland, it still felt forced and too convenient, I guess one just has to accept the "they are destined to be together" card and simply roll with it.
But what I hated above all was creating emotional dying scenes and even holding a funeral, just for it all to turn out to be fake, only for the sake of creating a cheap cliffhanger. It made me just wish they were actually dead. I don't mind the suspense with a grievously wounded lead like Seo Yul, but to fake deaths, that was such a sick move by the writers. Also in my humble opinion, you can create an epic saga about good fighting evil with the good prevailing, while still showing sacrifices and deaths on the good side, not every single character has to survive physically to be considered a happy ending. Just saying.

The pacing was not one of the best apsects about S1, but still overall it was highly enjoyable. But season2 easily outdid its predecessor in bumpy pacing, with 2/3 of the drama wasted running in circles of ( missed hints>confusions>angst>break up>making up>and back to more missed hints ). Although watching the two re-fall in love from scratch honestly felt fun to watch, the romance plot line just took comparatively too much run time for its own good, it reached a point where it felt clichéd and dragging I just wanted the big reveal to happen already (and when it finally did oh boy was it lackluster), and it also took away much needed time from the core issues at hand that needed to be addressed to insure a proper closure, those issues were only given less than a third of the running time, leaving us with 2 last episodes that are too rushed, one almost feels like gasping for air watching them, and with sudden shifts between scenes feeling like whiplashes. We are promised a grand and epic battle, only for it to end in mere minutes with every one watching at the sides in a safe environment and Jang Uk doing all the work. Honestly, nothing made much sense with that fire bird plot, evil plotting wise or how it was handled (if it is destined to hatch then let us hatch it earlier duh!)

the characters:
Our all so mighty ML who is supposedly feared by even the greatest of mages thanks to the power of the ice stone, was somehow rendered into a middle schooler both in emotions and inconsistency. Still his journey climbing up from the dark pit he had thrown himself into at the beginning, and how the FL helped warm and light up his world was endearing and heartfelt.
The bigger problem though was our FL, who was, even by her own words, foolish and weak especially during the first half of the drama. She had the face of Naksu (for reasons that made not much sense to begin with) so I would assume that most viewers were like me in hoping that she would regain her powers and we would finally be graced with more scenes of our bad-ass FL for a change , a prospect that was dangled in front of our eyes since the character was introduced S1ep01, but alas, we only ever witness a shrivel of Naksu in character, and even Jin Bu Yeon's powers are only ever displayed briefly. There were a couple of instances where I thought there had been an ample opportunity for the writers to choose to show her stand up and defend herself, to be deserving of the powerful souls that lies within her, like when after regaining her memories she decided to face Jin Mu, the man behind her madness and death in S1, and chose to dive into a treacherous place for the sake of beating him. I thought surely then she will somehow survive and come out on her own (after all we know that among the remaining powers left within her is the ability to cast away evil writhes and spirits), but God forbid no! they still chose to create an unbelievable sequence (involving coming up with the idea that she is the reincarnation of an old powerful mage) just in order to make the ML be the hero of the day and save the damsel in distress. Even in the final scenes of the finale, they totally had the chance to show that Naksu, whose soul had been spared the owner of the body, was working on regaining her long lost prowess. But no! The exact opposite, She adamantly expresses her absolute wish NOT to train, and to stay completely dependent on the ML. That was just disappointing tbh.

As for much of the side characters, they were mostly just that, side kicks stored on a shelf only picked up and utilized for conveniency's sake or to provide some elements of humor and immediately shelved back thereafter.
while I really liked how the crown prince was portrayed here and was somewhat satisfied that his character was thankfully one of the ones that witnessed a redemption, I can not still get over the fact that he left Jin Mu to become gwanju after all his evil deeds in S1.
Seo yul, felt bland as ever for the most part, but on a positive note his brooding sad expression here perfectly matched his lone wolf life in this season more than the previous one. The only instance were I felt emotionally connected to him was in the plot concering So I , which I honestly was moved and brought to tears by.
Jin Mu this season was too comical of a villain, he was powerless and totally dependent on his minions and other higher ups to realize his evil master plan (which was utterly stupid to begin with)

The acting
Superb on the most part.
A lot of people were turned off and disappointed by the FL casting. story-wise aside, I have to say I found her acting to be very good, especially in the second half when she had started to regain parts of her memory as Naksu. I also strangely felt more romantic chemistry in this season than season 1 (which made me feel kind of torn up), maybe owing to more physical intimacy and kiss scenes, dunno.
Seo yul was a nice cool dude but I have to admit I found the actor's portrayal to be a bit lacking, and how the character was written this season didn't help either.

I can't say I didn't enjoy this drama both seasons, but to be honest, I am of the belief that if there had been less filler plots in both seasons, both could have then been made to fit nicely into a 20 episodes format drama. Then I think with such high-end CGI and great casting, this could have easily been one of a kind classic.