I didn't have especially high hopes going into this. Most faerie novels and reverse harem novels I've found in recent memory haven't really done it for me, but I keep trying because I like faeries a lot and because I see the potential for interesting, emotional relationships in RH stories.
A positive in this novel's favor is that it isn't break-neck speed all the time--it takes several chapters to even introduce two of the four faeries who will be part of the harem.
But from there, it has a lot of the usual qualities of a basic RH: heroine starts feeling weirdly comfortable with and attracted to the guys even though they've developed very little familiarity or intimacy, even participating in physical affection well before they actually know one another, there's concerns about having feelings for multiple guys that's soothed over with one of them going "we're all close friends who like brothers, we're happy to share girls and are aware we all like you" or something to that effect, heroine is virginal/inexperienced yet expresses great sexual proclivity and desire that happens way too fast...
It feels a little too instalove for my tastes, we barely know anything about the princes and their time with Cassia is a bunch of repetition regarding monsters hunting her or them making some vague comment about wanting to protect her/be near her/etc. Only Cormac and Tristan are viewed as potential obstacles in the harem, with Cormac having a more closed off heart and Tristan being added very late in the book, while Ethan and Dane seem willing and eager to engage in any romantic or sexual activities.
Also, despite the book being about a 19 year old and it not being a purely clean read, the author did a fade-to-black after confirming that the first guy she's picked to have sex with "entered" her, so there's no detailed erotica.
One negative is also that we're not given much in terms of plot. The story is sort of... middling around, some battles here, attending a random wedding there, sleeping in another random farmhouse, riding more horses... I don't know what the overall plot is supposed to be; I'm presuming, purely on knowledge of these genres as a whole, that Cassia will end up being the next high queen with four princes as mates and she's probably part of some prophecy or Special Chosen One Destiny, but this installment doesn't establish much. Cassia doesn't pose many questions about why she was a changeling and doesn't express much desire to figure it out. Outside of hanging around the fae princes and sometimes wondering what her future holds, Cassia is a rather passive heroine.
I got all four books in a boxset for free (or was it 99 cents? One of the two) so I might continue with the next books just for the sake of completion, but I wasn't really impressed. Still, I don't think I'm going to put this on my "least liked RH" shelf because I've definitely read far, FAR worse with heroines I hated and plots that were insufferably dumb, so, that has to count for something, I'm sure.