I think this deserves far more praise than it seems to have received.
I'm from Sweden, born in the early 80s. I grew up with Astrid Lindgrens books and the TV-series and movies based on them. They are widely considered great stories, and I agree. But I cannot say that any of them really have deeply moved or affected me, including Ronja Rövardotter. Up until now. The fact that it took a Japanese animation studio for me to realize just how good this tale is says something about this series.
I was a bit skeptical to the visual style first, and it took a few episodes before I gave in, but after that, I just loved it. The cell-shaded style reminds me of The Legend of Zelda: Breath of the Wild, another Japanese masterpiece, and there is something beautiful to behold in almost every scene.
Studio Ghibli have treated this story with utmost respect and it shows that they really have understood it, which may sound trivial, but I think it isn't. The central characters feel very lifelike, with all their strengths, flaws, vulnerabilities, prides, fears and hopes. I can't imagine anyone doing a better work, and the attention to detail is just incredible. Just one in a myriad of examples: when Ronja goes skiing in the winter, it shows that they must have studied exactly how a person moves on skis.
Another thing I admire with studio Ghibli's work is that they have the courage to stay in a moment, and portray beautiful things, even small things like raindrops falling on leaves. Their love for nature really shines through, and it makes you want to also be in that beautiful forest - hadn't it been for the horrible harpies.
I watched this in Japanese with English subtitles, which I strongly recommend over the English dubbed version, if possible. I like how they have kept all the original names and to hear them pronounced in Japanese. Many of them sound strange also in Swedish even for a Swedish person; Astrid Lindgren apparently got most of them from a map of northern Sweden.
Thank you, studio Ghibli, for this. I'm very grateful. Domo arigato gozaimasu.