Want to know what I find really odd? Mermaid books are like contemporary books. I either love them or hate them, and it may or may not just be me turning into a picky reader.
I personally enjoyed the concept behind Fire of the Sea. There's Nordic mythology and mermaids, and I loved reading about the underwater world of unified sea creatures.
But there were just a few things that I really hated about the novel, and that was pretty much why I gave it such a low rating compared to everyone else I've seen on Goodreads. In fact, compared to the ratings I've seen on Goodreads and Amazon, I'm probably the lowest since I'm that weirdo who doesn't round up. (Not that I'm actually going to let that bother me greatly.)
Fire of the Sea felt more like a love story than anything else. Aeva, though loyal and courageous and torn between two worlds, was reckless and careless with some of her actions. Within several days after she saves Gunnar from being taken by the sea, she wants to leave behind her sea world and become human. Her reason? "I call it love because I don't have another name for it." It is, by far, the lamest reason I've ever heard. Her entire reasoning behind why she wants to become human is for love. A love for a guy she saved from the sea and should be a part of Davy Jones's locker, but because Aeva is a courageous mermaid who wanted to do a kind deed, he's not. Instead, he's tied to her.
It also felt like I was watching The Little Mermaid all over again. There's no prince, of course, but there's a mermaid (a princess, no less) who desires to be a part of the human world (though the reasons for each are quite different), there's a price to be paid to be human, and there's an Ursula. The Ursulas in the two are a little different, but Delphine might as well be Ursula simply due to the fact she can shift herself into an octopus.
Fire of the Sea was predictable, though that's beginning to not bother me as much simply due to the fact I'm ahead of the characters by a few steps. But in figuring out who Delphine was? That was a given, and I just waited to see if Aeva would actually figure it out herself before Delphine revealed herself.
So here's my final verdict: if you love a love story playing a major role with mythology and mermaids, you'll likely enjoy this. If you prefer mythology of the uncommon kind but don't care about the love story playing a major role, you might be peachy. But if you really hate love stories, then you might want to pass this up.