It's getting really formulaic. So, for every single book in every single series written by Rick Riodan, it goes roughly the same way. A threat that could result in the destruction of human civilisation. Then a new, bigger quest is hinted at and we learn of an EVER BIGGER THREAT TO HUMAN CIVILISATION FJDJSJDJDHAHSHSHALDKS, rinse and repeat.
After the first couple times being told that my darling protagonists are bravely facing the most dangerous danger, introducing an even bigger threat just... loses it's impact. My emotions get worn out, danger loses meaning. Riodan is trying to make the Triusomething sound significant it hopes that us readers will care about the story, but sorry, it might work the first five times but not now.
I was eagerly awaiting the climax of the book, when I looked at the pages and realised I'm already 90% through. There was some pacing issues, but I'm a poor writer myself and find it hard to identify the problem.
I wish Riodan wrote his books in Percy's universe in a way more similar to how Orson Scott Card wrote his books in Ender's world. At least for Ender's series, different books and different series have different challenges: some big some small, unique, but still relevant to the bigger picture. It doesn't have to be bigger threat after bigger threat. This isn't a damn d*ck size contest.