I tried really hard to keep at this book and I managed to finish it, thankfully, but no matter how hard I tried, I just couldn't get into it. The synopsis drew me in. A mermaid tale involving six princesses struggling to prevent an all-out war under the sea?! How can you not be intrigued?! But, alas, when I think of the execution of this story, the words "jumbled", "hodge podge", and "messy" come to mind. No matter how hard I tried, I just could not connect with the characters, and we all know that if the characters don't do it for me, there's little else that will save the book for me. In addition, the sheer amount of "mermaid vocabulary and slang/lingo" used in this book should've necessitated its own glossary or dictionary or something! It's not that I didn't understand what the words meant, but it irritated me how every other line was filled with the "mermaid lingo" and we were just supposed to go with it. It just didn't flow well for me. I felt like I was reading something in another language. I admire Donnelly for trying to be creative with her world and characters, but sometimes, enough is enough. 
 As for the story itself, there was just too much info-dumping and not enough stuff happening. While I appreciate getting to know this world and it is necessary in order to set up for the rest of the series, it added to the reason why I couldn't connect to any of the characters. I felt like I didn't know them at all. And even though stuff does happen along Sera and Neela's journey in finding the other princesses and escaping from the ones who are trying to kill them, each moment was short-lived and, really, just all over the place, I had a hard time keeping up. And it's not this is a difficult read either! It was just too confusing when it shouldn't have been at all. 
 I did enjoy it a tiny bit towards the very end when all the princesses come together, seeing how they work together and interact was interesting. I liked how Donnelly made it a point to include such diverse characters and how she embraced each culture. I was also captivated in the very beginning when we first meet Sera and her world. It started out decent, but then took a whole other turn, which turned me off from it. 
 I'm sure there are others who will enjoy, if not love Deep Blue, but for me, the characters just weren't engaging enough, the plot was rather dull, and the world that Donnelly created, albeit nice and magical, was too jumbled for my taste.