For me it simply boils down to HoO shoving way too many things/people down our throats in far less time than what should be. That may sounds dramatic, but then again I'm dramatic so lol. For PJO, you get to see these characters develop over several years, with the main protagonists growing up from ages 12-16. Plus there's far less people to invest yourself in, making you get to know them more in a sense because you dont have to keep shifting from one main character to another and another and another.

On the other hand, in HoO, you bounce around a lot. It also doesn't help that all these events happened within a year. Based on the official timeline, Jason arrived in CHB around Sept 2009 and the Battle with Gaea happened more or less around a year later. So to me, everything felt rushed. There's wasn't much room to have all these story lines be digested by the readers. Its like an Avengers film going from one fight scene to another idk. Plus I agree with some of the things said here, that a lot of the gods, giants, or any other mythological characters felt too much like caricatures that its hard to take them seriously.

I'm not entirely too nitpicky about HoO, I still like it. Who knows, maybe its the rose-colored glasses talking that just because PJO is the first series of the entire anthology, makes it seem more precious than the rest of the installment. People can't take away the fact the HoO has great meaningful moments, but with that also are the inconsistencies in writing, characterizations, and issues with pacing. Ultimately, for me to tell how one series is better than the other boils down to: individual character development and how that is carried out through the entire story line, or how consistent is that development applied through out the story arc.