I really don't see why this movie is rated so low. I've seen a lot of people upset about how little it follows the book, but book fans should know that the movie industry hardly ever keeps things exactly the same when they make a film adaptation of a book. Howl's Moving Castle is my favorite movie of all time. It didn't follow the book very well (and I have read the book), and yes it did receive some criticism from people who read the book before watching the movie. But it doesn't score nearly as low as Tales of Earthsea does. Why is that? Not to say that I think the two movies are equal; again, Howl's is my favorite. But it is to say that I think this particular movie may be receiving harsher judgement than deserved.
I have a lot of questions following the film and a lot of unanswered, but that is often true with Ghibli movies and I find myself having to rewatch the films over a few times to understand the true meaning.
I was deeply invested in Arren's struggle of light vs dark that was happening within him, and I was very excited to see what that special thing was about Therru that was being hinted at so much. Sparrowhawk and Tenar were very likable characters in very different ways, and Cob was a delightfully unsettling villain whose stare alone was enough to send shivers down your spine.
My only critiques: There were a few things that seemed out of place that didn't feel like they had any greater purpose in the end, which may have added to feeling like the story dragged on a bit. For example, the Queen in the beginning of the story. They camera panned from her feet up to her head as she spoke, which is usually more of a reveal that you would expect for a villain. This can be seen later when we don't see Cob's full face right away, and in other stories such as "Maleficent: Mistress of Evil" where the face of the Queen isn't shown right away, making it feel more like a grand reveal. I was highly expecting the Queen to have a much larger role. I also wish that more had been shown between Arren and Therru when she goes from hating or perhaps fearing him to caring about him. I think this could have been traded in for one of the other scenes that contribute to the slower pace.
Considering this was Gorō Miyazaki's first film, I think this was at the very least a decent film. I thoroughly enjoyed it and I'm excited to rewatch it and see if I can figure out more of the questions I had. If anything, all these questions are an opportunity to dive deeper and analyze, something I find both very helpful for your brain and also incredibly interesting.