Its quite good, I mean obviously it's different from what they do normally, however it's quite an interesting movie. I didn't read the book but the CGI is not horrible, and it's got an interesting story.
I don't see why this movie got such bad ratings because it has the Studio Ghibli name on it, and it's not their typical animation style? Nevertheless, it's still an alright movie and I would recommend checking it out if you have HBO Max or you got some spare time to watch a random movie, you might like it.