Of course any DT album will have some metal on it, just as any DT album has pop, prog and melodic rock. It's just a matter of how much of each "ingredient" is there. Falling Into Infinity and a big portion of Scenes From A Memory are much more rooted in the "melodic rock" and "pop" section than stuff like Systematic Chaos or Black Clouds which are very metal-focused albums.
The Astonishing, being a rock opera written specifically with that in mind, is more concerned with telling a story. And it's a story about relationships and conflict. The music is the emotion. So, there's a very wide array of songs, and very wide array of styles both between songs and within the songs. But the thing is, there's 34 songs. Whereas shorter albums have maybe one or two pop ballads, this will have many more. But it will also have many more rock songs and prog songs and metal songs. But of course, the people who are "just" into the metal part of DT will frown at the melodic songs on this one. Just like the fans of Awake frowned at Falling Into Infinity when it came out.
But this is the first time in 10 years I've really felt that DT has -changed-. SC, BCSL, ADTOE and S/T all were quite different albums, but they were also very much just evolutions of the stuff that came before. Not the paradigm shifts you had between awake and fii to sfam to sdoit to tot to 8v.