Lovely little story, with an old-fashioned feel to it that I rather enjoyed. I think for this reason many others may not enjoy it, but I found the time period it was set in really immersive, and the mer-mythology it was based around to have an appealing folklor-ish vibe.
The Forbidden Sea takes care to build up a complex history for lead character, Adrianne, and to give her cares and concerns outside being so utterly beguiled by her handsome love interest Denn, and falling in love with him. There is love, of course. But it feels less like the contemporary paranormal YA romance and more in the league of, say, Franny Billingsley. Because I love mythology and folklore, this appeals to me. If you like your teen para-love stories more contemporary, than perhaps you won't be as beguiled.
The Forbidden Sea has a little of the mystery I find so important for a story about mermaid/mermen. I just find these creatures so fascinating, most likely because the world they inhabit is so different and closed off to ours. This story goes a little of the way into giving merpeople a life away from, as I said, just being love interests. I also like how Nielson crafted Adrianne's interactions with the mermaid she thought was after her sister. It was a slow reveal. I love this. There was a palpable sense of being called to the sea - yes, yes, that's what a mermaid story should be all about!
I do think Adrianne being 'so hard done by' was a little over the top, and yet the details of her family life were welcome and also done in a way that made me actually want to see her come out on top. It was a rags to riches story that I kind of knew would turn out alright in the end. But Nielson made it worthwhile getting there.
The writing was on the better side of some of the YA mermaid books I've read. I'm slowly making my way through all those mer books out there and The Forbidden Sea, so far, is one of my favs. I've heard it described as a fairytale Little Mermaid meets Cinderella. Pretty accurate. Like to see what Nielson writes next.