I for one think it is great that this is solely Petrucci's concept storywise/lyrically. He seems to have had a very clear vision of what he wants and I think having him as the sole writer increases chances for a cohesive narrative and clear musical direction for the band. Normally I agree with people wanting lyrics from the whole band, but in cases like these I prefer the idea of the person with the vision giving the story content shape, instead of having other artists work within the boundaries of someone else's imagination.
It was initially a bit of a worry for me actually, that they were just having some fun in the studio and decided to randomly take a few popular intellectual properties and mash those story elements onto some DT tunes. But that is definately not the case here, which is great. This one has been in Petrucci's mind for quite some while. I obviously cannot speak for the quality of the concept yet, however.
Also, I think Labrie is a great singer to do the task of bringing the characters to life. I remember reading Arjen Lucassen said the way Labrie prepared for his role of Me in Human Equation was impressive; he really thinks his characters trough. And the approach Petrucci/Jordan took with the writing, more melodic and many short(er) songs, is likely to allow plenty of diversity and oppertunities for the different band members to shine. And then there are the choir and orchestra, which is awesome.