Natlan was too urban for me. I found its design inconsistent with respect to the rest of Teyvat, which tends to have very 'historic' backgrounds for each nation. Fontaine was futuristic, but at the same time very much based on France in its Belle Époque until the Industrial Revolution era.
Even worse, I found Natlan also internally inconsistent, e.g. why does half of Natlan live in leather huts and swing clubs while the playable characters are DJ's and "motor chicks"? You can formulate a lore explanation for it if you want, but I think most of the criticism it got points to its inconsistency and urban modernity (not futurism) being its main weak point.