I have mixed feelings about this book. On the one hand, I loved that it was a lot darker. Especially the idea of Percy experiencing

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the curses that vanquished monsters wished on him. Him having to deal with the consequences of his own actions, also with Bob, are really cool. This series focuses a lot more on the costs of war and the choices people have to make.

However, I feel the characterisation in this book was not great. Firstly, various people have life-changing experiences that really don't get mentioned after they happen.
Percy

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has a rather dark moment in Tartarus where he almost drowns the goddess of misery in her own snot (yeah it was scarier in the book) and Annabeth mentions it again once (in the 5th book) but it's never really a plot pointFrank

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is forever changed in Venice (and also he is no longer chubby) and we just move on. It's mentioned a few times, but it doesn't really change all too much

I found it hard to distinguish whose POV we were on, especially between Piper and Hazel. If we were in Tartarus, it was easy to figure out, but back on earth, everybody kind of sounded the same. That's pretty much the opposite of what switching POVs should do. The only people with distinct characters in this book were Leo, Hedge and to a certain extent Annabeth.

Nico is a whole other thing. He is described as scary constantly, but... I don't see it. Okay, so he can kinda melt into the shadows and pop up behind you unexpectedly. But I still remember him as the little boy from the PJO series. What changed? You can't tell me he has a scary vibe, I have to feel it. And I don't. The people around him have to tell me.

And then a lot of things seemed very convenient. I'm not saying Tartarus was easy, but

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Bob coming along was very helpful. And Hazel figured out her powers the moment she needed them...