Start with the scale, because it explains most of the arguments. Eight hundred thousand ratings on Amazon have it at 4.7, which is extraordinary for a 28-hour audiobook, and the readers who love it love it for the reasons people loved the first one: the training sequences, the politics of the quadrant, and a narrator pair that keeps a very large cast legible. A reviewer on Lemon8 put the positive case simply: "Reading Iron Flame was a rewarding adventure! Rebecca Yarros expertly balances character development with a magical storyline." The second half in particular is where the fans say the book earns its length, and several of the most common complaints about the first half disappear once the plot starts moving.

Now the other half, and the complaint that comes up first is size. The book is 623 pages in print and 28 hours in audio, and a reader in the fourthwing community summed up the fatigue in one line: "I didn't hate it, I do think it was too long and the ending wasn't really an ending." That sentence contains both of the structural objections at once. The first is that the middle stretches, with readers on Facebook noting that it only finds its footing around page 178, which is a long way into an eight-hundred-page experience to ask someone to wait. The second is that the book stops rather than concludes, and if you were hoping for a resolution you are going to spend the next year annoyed about it.

The other recurring criticism is the one about the central relationship, and it is specific enough to be fair. A long review on the blog Sprague de Camp Fan frames it carefully: the reviewer says they may complain that "the primary complaint of Violet for Xaden goes on too long", while conceding the rest. That is the shape of the objection across most of the negative reviews: not that the argument is unrealistic, but that the same argument is had too many times, in a book that has no spare room for repetition. It is also the reason Iron Flame has the reputation of being the weakest of the three: its Goodreads average sits around 4.36 from nearly three million ratings, noticeably below its predecessor, and the fourthwing community has a running thread literally titled why isn't Iron Flame as loved as Fourth Wing.

One thing to be clear about before you spend a credit. This is a middle book, and it behaves like one: the ending is a sharp stop rather than a payoff, and it exists to set up what comes next. If that is not something you enjoy, the honest advice is to have the third book ready before you finish this one, so the cliff is a pause instead of a wall.

Content-wise it is heavier than the first in every direction: more brutal training, more deaths, more explicit sexual content, and a stretch of psychological cruelty that several reviewers found genuinely difficult. Nobody should start here either. Begin with Fourth Wing, then come back for this. If you have already finished the series and want the day everything started, Threshing Day is the collection that finally shows Xaden's own bonding, and the guide to Empyrean Book Four is where to go when you start wondering how long the wait is.