You’re not reading a review of the third book in a trilogy to decide whether or not to read the series. You’re reading a review to find out whether or not the author sticks the landing. Whether or not the conclusion is satisfying. Whether the big questions are answered and the plot wraps itself up in a meaningful way. And the answer to your question is yes. In my opinion Kristoff absolutely nails it.
Without spoilers, here are some of the things you can expect from this book: Old friends from the previous books putting in appearances. New friends, because why not make a few new friends along the way. Pretty much every enemy you can think of also putting in an appearance. Pirates. You heard that right: pirates. Mythology and divinity revealed. True love. Epic battles. Derring do. Snarky footnotes. Sexy times. Cool assassin shit. Creepy blood magic. Watching characters you probably love die (if you think this is a spoiler you haven't read the first two books). Watching characters you probably hate also die (see previous comment). Leveling Up. Worldbuilding (yes, even in the last book). Some meta as hell stuff that made me smile. Plenty of action as well as brooding. And, arguably the most important part, closing the chapter on Mia's story.
Look, if you liked the other two books you will like this. And I feel it's safe to say that if you loved the other two books you'll love this one too. I know I did. I feel satisfied with the conclusion of this trilogy, and at the same time I'd love to read a new trilogy set in this world. And that's how I can tell it was a good ending.
Darkdawn hits shelves in September.