My overall take for the series is one I called from the very first book: it should have been a trilogy. The story has, admittedly, it's incredible and heartwarming moments; but they happen among repetitiveness and recycling that could've been avoided if everything was more condensed.
The points I enjoyed the most weren't really explored as deep as I would have liked, and as much as I can understand a children's book not wanting to hammer heavily about abuse I feel it would've been an important message to that audience.

I do like that it was at least touched on, that the Olympians aren't only neglectful parents to demigods but outright toxic to each other; in contrast to Meg's own form of suffering and manipulation. Apollo's growth and self-realization scenes were very well executed, making me able to disregard the pacing issues and just enjoy the moment.
The hopeful tone at the end, as sweet as it was, left a bittersweet feeling behind: Apollo has learned, but with his Godhood reinstated he feels distant from everything we've come to know.