Edit: Most of the review below is from the first time I read The Iron Trial, however recently I've been the whole "Is this a Harry Potter Rip-off thing" that many other reviewers have commented on, myself included albeit terribly. I was going to do a full re-review but instead I decided to just revise the section that talks about the parallels and comparisons between this series and Harry Potter. 
 Review: 
 Protagonist: Callum Hunt, often referred to in the book as "Call" (which by the way I really hated that spelling for his nickname, what's wrong with Cal? It's more commonly used and a lot less confusing) has been told his entire life, by his father, that the Magisterium, the school that teaches mages how to control and expand their elemental abilities, will lead to his death. So during the Iron Trial, the test that decides if you have the required amount of magic to be accepted into the Magisterium, he tries his hardest not to try, unfortunately his unrestrained magic comes out and he finds himself in the last place he wants to be. However while in the Magisterium he finds that it's not as bad as he thinks. Callum is a very complex character, as the authors have said, he bares all the markers for a typical Middle-Grade fantasy hero, however his destiny may not be what you think at first. I liked Callum's growth through the book, it felt real and his experiences at the Magisterium, while tiresome and grueling at times, were exciting to watch and thrilling to read. 
 World-Building: So, I have a few problems with the world-building, and it's not the whole "This sounds like Harry Potter" that everyone on Goodreads seems to be saying. First is the name of the main antagonist, "The Enemy of Death" or "The Enemy" for short. Now, that's all ominous and everything, but it's also way too cheesy to be taken seriously. Also, when we meet some of his followers they also refer to him as "The Enemy" which is really confusing as he is not their enemy and I have to remember what his full title is, but it still feels extremely weird for his followers to refer to him as "The Enemy" rather than something more ambiguous or more flattering like "The Master." All that aside however, while there are some places that I felt needed a bit more expansion or description, the world was fairly solid and was a joy to explore. 
 Predictability: So with the authors saying that this book was unpredictable I had my guard up, but still my normal foreshadowing sifter kicked in and at times I forgot that this was an unpredictable or unconventional fantasy story so I would often find myself surprised by the things that happened and at times felt like I was reading another side to the story I would typically be reading. The ending though was the most surprising of them all. 
 Ending: So once I got to towards the end I was reading what I had thought was a fairly normal and interesting ending, then out of no where, BAM! A huge twist materializes that changes the game so much that even though it wasn't a cliffhanger it still made me ache to read the next book as soon as possible. The actually ending was rather plateaued and expected but did nothing to stifle the curiosity that I feel for where the next book may lead. 
 Is it a Harry Potter Rip-Off?: The short answer is no, the long answer is a bit more complicated. So while I admit there are definitely parallels between this book and the Harry Potter series there is much more that's different. First off is the characters, while many of the characters fit into certain archetypes that also line up with characters in the Harry Potter series, such as the nemesis and the wise old mentor, the backgrounds of all these characters are wildly different from their HP counterparts. For example, Tamara, the know-it- all female best friend character could bare a striking resemblance (character-wise) to Hermione, but the reasons she knows what she does isn't because she studied it on her own to try and get on par with the other magic students but because her family has drilled it into her and she in actuality just wants to succeed and have fun doing what she wants. Both these characters are alike on the surface, but the have different backgrounds and different motivations. The same thing with the world building, in the most general sense it's exactly like Harry Potter, a world where certain kids can study magic at a special school, but if you dig deeper, and honestly you don't have to dig that deep, these books are very different in many ways. 
 Rating: 
 So after careful thought and consideration I'm giving this book 4 stars. It's a powerful and epic story, but there were a few things I couldn't get past. In addition to what I stated above this book moved a bit slow at times and I felt that Callum's Master took a bit too much of a "wax on, wax off" approach to his teaching instead of after a while teaching more up front and direct elemental techniques.