Having read The Olden Chronicles first, I have to say that I absolutely love being back in this world. Having my heart ripped from my body in Crimson Tears, it's good to know my favourite characters have not been forgotten!
Finn, as promised, is just like his uncles, and Freya is a carbon copy of her mum. It was just destined to be that the two of them would end up together. You can't keep the Raghnalls and the Oldens apart for long. 
There are reminders and snippets of characters from the prequel series that I know will come to more in the next books!
As per usual, I have to remind myself not to get attached to side characters because Shauna has an itchy trigger finger that keeps you on edge, but it's hard when they're so good! 
I detest the Pretons, especially one in particular, and I hope a ghost comes back and ends him slowly! 
A lot goes on in the book, and its pace is quick. There are multiple pov so you have to pay attention.
I'm glad I read the Oldens first. I knew their family and their history, and I don't think I'd have felt as connected  if I didn't know what happened when these kids were younger. So I would absolutely recommend reading Shattered Steel and the rest first before reading this trilogy. It will be more of an experience. 
Shauna'a writing style is easy, mixed with humour and dark themes, and I flew through the story. I can't wait to read book 2!