i can definitely see why people compare this to Harry Potter. but i also think whenever you have a middle grade fantasy and a magic school, your natural inclination is to compare it to Harry Potter. yes, there are a lot of similarities, but it's pretty different too. 
 Plot- compelling. i didn't want to stop reading. 
 Characters- i looooove Aaron. he's probably my favorite right now. but as usual, i also love the friendships between the main 3. i can't wait to see how they grow. all of the characters are unique. and it's kind of nice that so far, there's none i actually hate. 
 World Building-so far it's pretty good. i think the magic system is pretty interesting. i can't wait to read more about the mages outside of The Magisterium. 
 Diversity- LOADS! MCs of color, and Call has a disability. his leg was shattered as a baby, so he deals with chronic pain and a limp.