TLDR: Pretty good, if you can treat it as a standalone thing instead of tying it to the books (but while still understanding the world that K. le Guin built). Has flaws with storytelling but doesn't deserve to be rated so low.
FOR THOSE WHO HAVE READ THE BOOKS, PLEASE READ:
This movie, as a stand-alone movie, is not very good. Much goes unexplained and mysterious, which tends toward bad storytelling for those who have not read the books. If you have not already, I HIGHLY recommend reading the Earthsea novels before watching or many things (character relations, settings, key plot points) won't make much sense.
For those who HAVE read the books:
This movie stands apart from Ursula K. Le Guin's novels. Think of it more as a parallel universe with a related but different story. Much of what is referenced in the movie will make sense to those who have read her books, but if you're expecting a faithful re-telling this is NOT it.
If you can manage to separate this film from the books, then it's pretty good. The plot is enjoyable high-fantasy and doesn't offend at all. It's not by any means a masterpiece, but it's beautifully animated and had a solid soundtrack to boot. Some of the characters could be more fleshed out, but it's pretty solid overall. Most of the gripes people have with it are valid, but they seem to come from people who either haven't read the books or HAVE read the books and are expecting a faithful retelling.
(Spoilers ahead, do not read if you have not read the books)
The only MAIN issues I see are with the plotline of the doppelganger and the dismissal of the first book two books of the series. There's no explanation of who Tenar is; they made her far more insignificant than she was in the books, and the doppelganger isn't explained very well (I.E. where it came from, what magic brought it into play, etc.). Ged/Sparrowhawk is now a secondary character to Arren, but honestly, I'm okay with that.
As for Cob - Many people seem to be complaining about how they had a poor explanation/background, but in the original books they were only really introduced in the third book as a novice wizard with some very powers who happened to have a grudge against Ged, so I don't think they're lack of intro was anything the original books were lacking anyway (this is a personal gripe I have with the books anyway, Ursula did a bad job with his character I think.)
The film follows (sort of) book three with elements of two and four thrown in. It could have done a better job of explaining the magic system and what's going on in the world, but if you separate it from the books as its own thing it's genuinely very enjoyable.