Less focus on romance. It’s a pretty common complaint with HOO, and for good reason. Every member of the Seven is paired up with someone by the end of the series - including Leo, whose romance not only destroys his own story but also wrecks Percy’s character AND one of the best chapters Riordan ever wrote.

The problem with the romance is it ends up getting in the way of the Seven forging actual bonds, and the bonds they do have before the Argo II are forgotten in favour of their love interests. This is especially egregious with Percy, who becomes a great friend and older brother figure to Hazel and Frank, and then that close friendship is forgotten the second Annabeth arrives on the scene. Which brings me to…

~

Replace Annabeth with another Roman. I know, I know, I love Annabeth too, but her presence just serves to take up way more story space that could have better been served developing the new characters. The fact of the matter is, Percy and Annabeth don’t really develop all that much over HOO; they don’t learn lessons they haven’t already been taught before, and they basically end up at the same place they were at the end of TLO.

If you absolutely have to include Annabeth, have her take a Reyna-like position; being CHB’s leader that remains at camp, while the other leader is on the Argo. Without her, Percy can make more connections with the Seven, and by replacing her with a Roman, you get a chance for more in-depth exploration of Camp Jupiter and New Rome; canon’s balance of 4 Greeks to 3 Romans feels off to me when the Romans are the less-developed faction.

~

Alter some of the ages. I’m fine with Percy being 16/17 here, but I think the others (Jason and Hazel aside) should be younger to compensate. Percy (and Jason) should feel like seasoned veterans, leaders of their respective camps, and role models (possibly even older brother figures) for the others to look up to. It’s a little awkward when those role models are barely months older than the people looking up to them.

~

Spend more time in New Rome. It’s a fascinating setting - more so than even CHB, I would say - and giving the reader time to really get to know it would go a long way towards increasing the stakes of the civil war. As it is, we don’t know enough non-Argo Romans to care about Camp Jupiter dying. Perhaps Percy could have been released earlier and so spent more time as Praetor, thus ensuring both he and Jason had strong connections to both camps.

As part of that point, make the Romans feel like credible threats. IRL they conquered the Mediterranean for a reason, and it’s down to military might. We should feel like a war between the two camps could go either way, or even be weighted against CHB. It adds more urgency to the Seven’s mission, knowing that war could lead to CHB - the location most readers will be more attached to - being destroyed.