What about the Greenwood makes it so sought after? It can't just be because it's OOP. And I'm sure there were Celtic spirituality decks before it, weren't there?
It's only my opinion. But I think - the art in a particular tarot deck reflects something of the soul of its artist. My feeling is, that the Greenwood is a very honest tarot, here no one wants to get applause. The core is the love to the nature, the being per se. It's a deep deck, created from someone who has a deep connection to herself - that triggers a deeper connection of the beholders to themselves.
For me it is so like the artist draws paintings, completely absorbed by her work and concentrated while gentle singing a song (like a child, who knows the secrets of the world) - and we can hear the song if we look at the images. There is something of truth in it what is not so easy to find in other tarots.
Oh, was a bit off topic. To be honest, very much of the expensive decks I don't want. I was looking for special things the decks had to have. Something that is able to resonate with what I'm seeking in tarot. I found it, but for me it is not very often to find. But I think, people are seeking different things in tarot decks. That would be an interesting question for the talking area: what are you seeking in tarot decks?