I found Heir of Fire much more engaging and enjoyable than I did the first two in this series. While the moping and feeling sorry for themselves of the 3 main characters was a little overdone and drawn out for me, the characters started on their journey towards growing up a little and the ending of it gave me hope for the 4th book in the series. I did do a review when I finished the book for some reason it has not appeared on the site in the last week, so I'm doing it again.
I found the addition of 2 new characters really gave this story the shot in the arm it needed. Manon, the witch and Rowan the immortal fae warrior are both very strong additions to the cast. They're also a strong juxtaposition between the three main characters who aren't 100% sure what fate holds in store. Manon and Rowan are about as immovable as mountains, both convinced they're exactly where they need to be and are bullet proof.
This novel contains much more of Alien's heart and soul story. Hearing about the fall of her country, the deaths of those around her and the pain she carries makes the character a little bit more relateable (?) and likable than she has been previously.
Over all I found Heir of Fire moved a much quicker pace and was well written, engaging novel.