I don't care much for superhero stories, but I generally like Brandon Sanderson's writing, so I followed up on this series. It was disappointing.
The writing seems to lack Sanderson's usual flair. There's quite a lot of clumsy prose, especially at the start. The action is simplistic and over-explained, and while some of the humor works, much of it is overdone. The dialogue works too hard to be clever, and it doesn't feel realistic.
The basis of the story itself - the magic system, if you will - remains interesting, and the characters are engaging. It's just hard to get to it at times. Overall, the story feels like an early draft that still needs considerable polish. If it weren't for The Rithmatist, I'd just think Sanderson can't handle YA. In fact, though, his usual style is very accessible, and I'd argue he'd be better off just using that style with these characters.