This is not a classic revenge story where the protagonist chases the antagonist in a straight line. It's hard to put it in words without spoiling, but you'll see once you give it a chance. It's a nice spin in the revenge genre with an interesting premise and good world building.
Characters are very well written, specially the growth and progression of Gwiyoung, the main character, and how he faces his deep rooted trauma and extreme hate for the barbarians. Asides from him, every other significant character is also complex and written in such a manner that it's hard to truly guess what's on their minds.
Neither side is black and white, bad or good. You can sympathize with both and see their wrongs.
Art is nice during the first season, with amazing environments and panel design, but characters looked cartoonish at times. Second season improves on everything, might be Top 10 in terms of art, even though there's no flashy magic going around.
8.5/10 for now, I'll update it as the story progresses. Great read, but it can be confusing if you look at it without any insight.
(If you're one of the apes that gave it a 4 or 5, watch your back)