The design is a bit underwhelming. It looks cheap. Maybe not exactly cheap, but let's say simplistic, almost minimalist sometimes. And the colors all look a bit passed. It feels like something from 30 years ago instead of 3.

So I went to look back at the first episodes of the webtoon, and yeah, graphically it's a bit lacking, but come on, it's been 10 years, how the fuck do you decide to base your anime design on the first 10 episodes of a series that is at nearly 600 now ?!
The drawing improved a lot and it's gorgeous now. Why not use the current design and go for the oldest drawings ??

This is a huge disservice to the show and the original material.

Animation is not great either.

However it seems pretty much in line with the original story (or at least what I remember, it's been more than 10 years since I started). And the original concepts, the multiple characters and the complexity of the story (season 1 is not even the tip of the iceberg), more than make up for it.

Hope they continue, but one season every 4 years, it will be hard to catch up...
Why so long ? Specially as the production value looks pretty cheap, looks like something they could mass produce like animes from weekly mangas.
Unless it means they redesigned and improved the quality for season 2, which would be awesome.