Ori and the Blind Forest
I think the setup for this is painfully simple, but that doesn’t mean it can’t be an incredible series. Ori is an orphaned young spirit guardian who must learn the ways of the forest and how to restore it from a calamity, sounds like a really easy setting to make an animated series out of if you ask me.
The series itself, depending on if you wanted it to be something limited or something that goes for at least several seasons, could easily be about Ori and learning how the forest works and how important each element is. He could encounter new threats to the forest that teach him new lessons on how to be a better guardian.
However, beyond that what would be vital to making an excellent series based on Ori and The Blind Forest more than most on this list is that it would have to retain the same hauntingly beautiful but also wondrous animation and music.
Most of the other series on this list don’t necessarily need that, but it’s such a core part of what makes Ori and the Blind Forest so memorable that if a series based on it has nothing that evokes that, it doesn’t work. So if a series were to happen, hopefully, they keep up with the quality animation and music the games are known for.