I get the sense that JP enjoys writing about human topics. Topics dealing with humanity, more so one's mentality. This mentality can be both physical such as anxiety and mental illness, and spiritual such as the afterlife, philosophy, and the struggles of humanity.
Now that you mention this, it makes his lyrics for Systematic Chaos feel more fun now, and stuff he wrote for kicks and to just have fun lyrically and musically, like The Dark Eternal Night and Forsaken (and I find it pretty interesting how the verses sound like the verses in the song "Cold" by Static-X, which was coincidentally used in a movie about vampires, Queen of The Damned).
The Astonishing combined both this Humanistic lyric style with his storytelling fun of Systematic Chaos. Which I found great for what it is, as JP is not a genius with words. But it works for the dialogue of the characters and the narrator. I do like how this includes his humanity and Mental Health with regards to how integral music is for humans. By showing the mentality of people who hear Gabriels' music that it has healing qualities for them, it helps them mentally.