Commanding the Tides is an Atlantis/mermaid romance story. That's probably the first and biggest thing you should know. No spoilers or anything, that's pretty much the premise. If you're a previous Michelle M. Pillow reader, you'll know that her romances aren't clean but full of lots of naughty romping. This one is no different, so beware and/or enjoy. :) This is book 2 in the series and I feel you could probably jump in here and have no issues. The first two characters from the last book are in this one, so you'd know them better if you did, but it's not mandatory to enjoy the story. Written in third person omniscient from both leads' perspectives.
These mermen...they're just giant softies! But I guess a few thousand years without regular female company might make anyone a bit hungry for affection. Iason was super sweet. There's really no other way to describe him properly. There is definitely something of a fated feel to this romance, and he goes whole hog, all in, yes please! I actually feel bad for him when Cassandra says or does things that he doesn't understand (yeah, that trait follows species, apparently).
Cassandra, for her part, is an interesting character. Dying of bone cancer when the boat she's on is sunk, she's quite prepared to die. Her attitude and demeanor throughout the book is tainted by her years of living with such a debilitating degenerating condition and it certainly makes for some interesting misunderstandings. Overall, I liked her much better than Bridget-she felt more well balanced.
Their relationship is a very soft and squishy one that gives you all the feels. They of course face some problems (crazy mermaids again anyone?), but they do eventually get their HEA. There is a small amount of action, a LOT of steam, plenty of gooey moments, and some interesting fish to boot! If you want an interesting merman story with lots of steam, give this a go!