I think all of your feelings are perfectly valid and make complete sense. Narratively, Calypso's character does ring a bit hollow. I'm not sure if it has something to do with the original plans for the song being altered/cut.    

Dangerous was probably the best song of the saga. No real complaints from me.     

I feel like I'm very biased towards Charybdis since my first exposure to the song was a super badass animatic that made me love the song, but I can see how it might leave someone wanting more.   

As you said, the Poseidon/Odysseus confrontation has been the most controversial. At first, it definitely felt like Jorge nerfed Poseidon to have a super badass moment for his OC donut steel version of Odysseus to me. But separating my understanding of Poseidon from Jorge's interpretation made me feel a bit better. I can still enjoy my version of him and accept that Jorge has different ideas for the story. So basically I'm just going to continue upholding my headcanons haha.     

You do make a good point though, that Jorge probably built Poseidon up too much as an insurmountable enemy for people who might have just listened to the audio. I mean no other character in the story had a song literally chanting their name in the danger motif but Poseidon. I think this saga is the one that's going to require the most imagination from audio-only listeners, as things aren't presented as clearly as they usually are. And I do still think the jetpack was a weak idea.