The concept of this book grabbed me right away. Genetically engineered sea monsters and pirates are an irresistable combination. The futuristic world hinted at is interesting and I wish we had more of a chance to explore it. Unfortunately, except for the first chapter and a brief visit to a floating city, the entire book takes place on a single pirate vessel with little mention of the rest of the world. 
 There are many things to like in 'The Abyss Surrounds Us'. The monstrous nature of the Reckoners is not shied away from and they truly feel like leviathans from the deep. The writing is clear and easy to follow and Cas's voice is likeable. The story moves along briskly and displays a balance of action and character ruminations. I found the love story sweet and liked that Cas stood up for 'equal footing'. 
 A few things kept this from being a 4 or 5 star book for me. As previously mentioned, there was not much exploration of the world, even from the pirate point of view. In the several months Cas was with them, they only seemed to raid one ship - an event that disgusted her at the time, but that she seemed to get over quickly. In general the pirates seemed a bit tame. Although we were told several times that Cas's life was at risk if she didn't stick close to Swift, there were no close calls or other evidence to back this up, so it was difficult to feel too worried for her. In general, a lack of tension made the middle of the book a little slow for me - it seemed like a lot of Cas worrying for no reason. 
 Until the end of the book, Cas was quite reactive as a character. She didn't fully commit to either her 'good' side or her 'monster' side and even after making plans to justify staying on the ship, didn't seem to do anything to fulfill them (and the answer falling into her lap instead). It was a little frustrating to see her do something that she knew was immoral (because she was afraid of getting hurt), then as soon as she had irreversibly done it, feel terrible about it and try futilely to reverse things. 
 Past those details, this is a solid adventure story and a nice evolution to the 'girl and monster' category. It has a little to offer everyone, with romance, sea battles, and creatures out of legends.