Surprisingly really good!

I see what you mean about the poster. IMDb have changed it when you look up the film on their site. It shows the ship with red sails being pursued by that scaly looking monster. I think it's the monster that looks like a giant crocodile which I've seen in the trailer.

I wonder if it was meant as a theatrical movie but Netflix got to it first.

I'd give it a 7.5/10. The first half is stronger, but the second part is solid enough and the ending is heartwarming.
It's funny that the viewership ratings are apparently excellent cuz I thought the marketing for this sucked. Like it seemed they were focusing on the comedic bits in the second act or making it seem exactly what you said, a cheap knock-off.
Despite it being nothing of the sort. Thank goodness. In fact, while it is still stylized, the animation looks damn near Pixar quality in parts.

I agree with you more. I'm not calling this movie overrated, but I wish the rotten tomatoes score would have at least been over 80% as opposed to the 94% score it received.

That being said, this is a good movie overall. So what if some parts of the movie could've been fleshed out more? So what if it does feel like a mix of Treasure Planet and How To Train Your Dragon? Everything else is interesting. The concept is creative and the first half is very strong, establishing the setting and characters very well. Maisie started off as somewhat annoying but she did get better later on in the film, Jacob is also likeable thanks to Karl Urban's superb voice work, and the other side characters are fine just the way they are. Not to mention that it's rare that a Non Disney animated feature film has moments of blood and some language and yet still has a PG rating (throw me on that one).

I gave it a 7/10.

The animation is quite good, the characters are all interesting/ok.

However, I would have enjoyed a "cooler" beast, I didn't really like the design of it.

It also felt like a cheaper version of How to Train Your Dragon, without a doubt, and it was too preachy.
The ending was too tidy and not realistic (in terms of characters reactions).

And the conclusion is that... "Humans will never explore that area of the sea and that's ok". Seems a bit weird... Humans are explorers and should always have all the information they can get.