Binged watched both parts in one day without any expectations or spoilers previously.
If you like comics, webtoons, anime...etc. with thriller, fantasy, horror and action as themes than this drama is made for you.
Do not expect a typical drama.

Acting was excellent. There was no boring moment or episode. Many exciting and visually beautiful actions scenes.

More than any other thing, I loved the whole atmosphere of the show. It really gives a "watching a webtoon becoming a movie" kind of vibe. So many moments and scenes felt like they were filmed just the way they were drawn and I had to replay them to enjoy their beauty. (I love comics and webtoons and haven't seen this one before but I know that kind of scene when I see one)

The story progressed in a steady and exciting pace and it was very easy to enter this new fantasy world together with FL.
New elements, discoveries, background stories were added one at the time so they would be both exciting and easy to understand. There were two moments when I felt the story is somehow disconnected but I quickly realized that things like that are exactly what happens when you read a webtoon and ended up liking that disconnections b/c the whole vibe became stronger.

There was no reason to split this one in two parts and it really should be rated as one 12 eps drama here.
One background story remained a mystery and there is hope for part 3 or a separate drama.