Strictly speaking, I would give the first and the second books 4 1/2 stars; as it is I gave the first book 5 stars, leaving the second with 4. This is much darker book, but still a very enjoyable read. A minor annoyance: there are less interactions between Hadrian and Royce (they are forced to work separately most of the time) which made first book great.
Having said that, I still think the book is great, and it makes you want to read the last two novels of the series. If you read and like the first book, this one is a must.