This show is a strange beast, because a lot happens in it, but it seems like less would be more in this case.
First, THE STORY:
1. This is distinctly a fantasy show, and there is a lot of world-building that is happening -- maybe too much. Not sure if this is a translation issue (though I do not think that is the case), but a lot of elements are introduced that appear extraneous and distract from the main plot. The confusing bit is that the viewer does not know which part will be important; at first I tried to keep track of the terms and ideas, but after a few episodes I let go of that and just let the plot develop without really trying to follow it too closely; that helped.
The story tries to establish that the main character is "extraordinary" because he manages to learn skills faster than others; this may have been impressive, except it is not clear what those skills really are or how he actually mastered them (the whole catching the fish thing was so unclear -- was it cheating? what did he actually learn in order to do it?). It felt a little like someone telling you that a song was the most beautiful ever written and expecting you to absolutely love it without hearing it or any other song ever.
2. I know this is asking a lot (and I am not being facetious -- it really is asking a lot for a complicated story over 20 episodes), but the "reality" of actions and reactions is tenuous. E.g., the female of the Four Seasons virtually sends the female lead to her death, and yet not only are there no real consequences for her, but also the audience is made to quickly get over and forget it.
3. Finally, the romantic tension. Don't get me wrong: The actors do a very good job interacting, but (related to point #1), at some point I lost track of what the heroine said she would do once she regained her powers and why (and I kind of stopped caring about the specifics). There will need to be a decision? or something? that will force the characters to separate? But is that something they can decide to do? Or something they would absolutely need to do? Something like that. Right now, it just feels like it's some kind of internal struggle thing for the heroine, but it feels like nonsense.
Regarding the ACTING, as stated, it's generally good.
The MUSIC is OK.
There are only two episodes to go, and I will absolutely watch them, but I do not consider those 20 hours well spent and cannot in good conscience recommend that others watch the show. Which is a shame.