Across the Green Grass Fields is the sixth installment of McGuire's Wayward Children series, touted as being a jumping off point for readers new to the series. I think perhaps this is why I felt so underwhelmed by it in the end -- the novel follows the same basic set up as many of the others, where a child has a difficult time at home, then comes across a door and enters another world that seems perfect for them, only to wind up being sent back to their original world. As someone who has read the entire series, it just felt like taking a step back in how the stories have progressed from the first novel which introduced us to that set up.
Usually I find McGuire's imagination and creativity enviable, but here it fell flat for me. Maybe it's because I never went through a horse phase as a kid -- I think the closest I came was watching The Saddle Club on TV and maybe reading a few of the books -- but McGuire's worldbuilding was thin here. Regan spends most of her time hidden away by her centaur family, which is full of characters that are likable, but that causes the world to feel small. There's a bit of worldbuilding at the end but it's rushed, as is the third act of the novel. Regan doesn't get to explore the Hooflands, so it doesn't feel lived in.
I do however like that there was representation of intersex people in this novel. This is still one of my favorite series and I'll read whatever McGuire writes for it. Across the Green Grass Fields just isn't my favorite of the series, unfortunately.