Why can't we all just get along? [EDIT: I was being facetious here, but it didn't translate, so hence the neurotic edit. People can think what they want about the album, just thought of giving my two cents below]
As much as I love The Astonishing, I don't know how to make a case for it. It is a big ask -- I think the band tried their best to onboard the fans to what is arguably a freaky experience: equal parts Dream Theater album and cast recording of a broadway musical.
It is likely the most Jordan-esque of all their albums, even if JP wrote the story. I think the signs in their history that point to what they went for in this album have been there since SFAM -- take the start of Finally Free (and first verse), the whole structure of SDOIT (the track), particularly the Overture and Grand Finale, and The Astonishing ends up feeling like a culmination of that type of musical storytelling.
Not for everyone and, really, perhaps the least Portnoy-esque album in their career, in the sense that he might've (not saying for certain, just a hunch) said "no" to a lot of the ideas from the early stages. Or perhaps the antithesis of a song like "As I Am", if that makes sense.