First off, I would like to say I liked Nerissa - she is sassy, no-nonsense, knows when to pick her battles and doesn't create much drama - even though being a teenager she is prone to occasional fits of rebellion. She comes off as arrogant and spoiled at times, but if you were the sole princess whose every whim was catered to from birth, wouldn't you be too? In the beginning of the book, she feels vulnerable and useless because of her past attitude and her inability to go back and claim her throne. She would prefer living in the human world, but when her enemy brings a challenge to her coast, she can't back down. Keeping a human cover and avoiding a certain human boy whom she has an intense attraction to - so not easy.
The writing was brilliant and as I said before, I loved the alien theory mixed with an ancient lore. The storytelling was spectacular and the twists in the story kept me hooked. The romance was intense, yes, but fit the storyline. The forgiveness theme played a lot in the book and while I felt the Cara arc didn't do much for the main plot, it was good for Nerissa's development. The flirting/banter between Nerissa and Lo is quite entertaining, though the end had me feeling bad for Lo. I was grateful that I didn't have to choose - a love triangle would have been overwhelming and it's good that Howard had the foresight to avoid it.
Now, about the role the Aquarathi play - that one had me a bit meh about it. It wasn't properly explained and I don't see why only the royal heirs have to do the ambassador business - why can't some members of the Aquarathi have occasional trips to the land and help foster marine conservation. Considering the health of our oceans is in such dire situations, they can do better than just send their teen heir, like one in a generation - it is too little to contribute, don't you think?
Overall, I found this to be a great book and I loved the fresh take on the mermaid legends.