The API has been discontinued, but it's actually faster to collect reviews from RSS feeds.

If there's interest, I started a script here

https://colab.research.google.com/drive/1uOyVlKaT4QFtce9yQpKj9hRtj5z8Uyta

It still needs work in confirming it has gotten all the books from a user (I think there might be timeouts) and issues with books that have several versions/editions. But the biggest bottleneck is collecting reviews from all 100 million users