The beginning is a bit slow, I will admit, but the first season is a very good adaptation overall (later seasons skip a lot). So maybe it’s just not your cup of tea. I don’t think I follow the base-building analogy 🤔

As for its popularity, I think it does a lot of things really well, better than most other series, and the sum of it is superb.

• Characterization: there are almost no 1-dimensional characters. Even random side characters, or seemingly comic relief characters, have their own motivations and goings-on outside of what Myne (the unreliable narrator) sees. These are often revealed to the reader in side stories, and can recontextualize a lot of what’s happening.
• World building: we start with a straightforward medieval city. Then a small bit of magic is introduced. Then we find out about a bit how the country is governed, then more about how magic works, histories, politics…all in a satisfying way, because Kazuki-sensei planned the whole story from the beginning. Which brings me to:
• Foreshadowing: EVERYTHING is a Chekov’s gun. There’s a lot of stuff to find on a re-read, and the theorycrafting people come up with in the weekly chapter releases is a lot of fun too.
• Themes: this series does not shy away from serious themes. Poverty, children starving, sexual assault, the ramifications of a strict caste system, slavery…There’s a lot that sucked about medieval times. But also:
• Humor: absolutely great comedic moments. It’s rare for a book to make me laugh out loud. For example, there’s a scene where Myne hosts what is essentially a J-Pop concert and it’s just nuts.

I could go on…tl;dr it’s a great series!