If you like the naval battles and pirates stories it's great. Otherwise, the same AC mechanics, the story is somehow ok, I liked the economy part in the game, small cities and small islands in general, so not much to explore on foot for most part of the game, but huge sea. The character is less horrid than in AC III. I enjoyed it for some time. I should get back to it actually.
It looks good on Wii U and except for some fights with many guys on the screens at the same time it plays quite well too. Even then it's not unplayable. It's a good game for screenshots.
And Child of light is indeed really good, I'm playing through it right now.