I'm not gonna lie and say this book (and the series) was average all through. I was engaged, it was interesting, and as a good slow-burn enthusiast, I was invested. The mood of the story is incredibly well done, something I find more and more an important characteristic of self-published books. This amount of self-indulgence akin to fanfiction is something very rarely replicated by books that go through an editorial process.
But the trade-off (here and frequently in similar situations), is a very flawed execution. Oftentimes the plot and pacing jump around like they're not sure what they want to be, characters' motivations and personalities seem inconsistent, and the conclusion is very lackluster. The ending was so jarringly abrupt I was sure my kindle file had lost it's epilogue. (No, releasing a post-canon book of tales does not excuse the lack of proper conclusion)
I think the best description I have for The Captive Prince series is that it certainly is an experience. It requires a specific taste and mood to be appreciated, and an hability to shrug off the flaws and enjoy the ride.