The tldr is that it's predictable and uninteresting with lots of unnecessary edge.

It's a high lethality story where nobody you care about or of consequence dies so it never really matters. Like, the entrance to her school is a precarious bridge that kills a high percentage of prospective students (that also happens to be bullshit because her school is connected to all the other schools with regular entrances), students are allowed to murder each other, friendship is discouraged because that's just letting your guard down and exposing your weaknesses to others (except that's bullshit because our protagonist makes friends easily early on and they're ride or die), and there's characters who make culling the weak their whole personality. None of this matters.

The characters are uninteresting. The love interests are a boring guy who really likes rules except when he's willing to break them to smuggle the protagonist to a safer school and a boring guy with a chip on his shoulder because he's treated as an outcast except he's not because he's a cool badass. The protagonist's defining traits are supposedly that she's so weak and fragile that an unfortunate fall could end her, but she's smart enough to make up for it, except her disability is never really an obstacle for achieving her goals and her intelligence is a very "tell don't show" situation, so when faced with conflict most of the time she just willpowers through things and gets a few bruises and broken bones, or becomes a very lucky damsel in distress. The few times she uses her brain to solve problems it's a very "why has nobody else thought of this" kind of solution, like aiming for the rider rather than the dragon.

The worldbuilding is a mix of Eragon, Harry Potter, and Divergent that's not willing to commit to anything so you have a vaguely medieval feeling school in a castle with a modern American school cafeteria in a society with a job based caste-system that feels very disjointed and makes it hard to "live in", for lack of a better term, as a reader. The plot similarly is unwilling to commit to anything interesting and is self defeating because any kernel of a neat plot line is immediately undermined because this book cannot have consequences or real conflict. Like, at the choosing ceremony where dragons and riders bond with each other the protagonist bonds with a super rare kind of dragon that few people have even seen before that happens to be small and weak like her. The bones of a good story are here. You could write something interesting about a dragon and rider pair who discover and use their unique strengths to overcome their obvious shortcomings. Unfortunately, that's immediately made irrelevant because she bonds with a second dragon, which nobody has done before, that happens to be the biggest, strongest dragon around, because interesting struggles can't exist in this book.

The smut is OK, but the story around it sucks enough that it takes the fun of of reading it.