When I think DT masterpeice, I don't think 9 albums. to me, a masterpeice is a very uncommon thing that sticks out due to uncontested greatness. Granted, everyone's idea of what a masterpeice is, is different, so you have to incorporate somewhat the general consensus. for example.
ACOS
6 degrees (the song)
what i mean to say is that while you might not "like" those songs, they are undoubtly some of Dream theater;s best work. So, do i think that dream theater have produced anything comparable to those two since six degrees? in my opinion, no. That's not what to say what they have produced since then isn't awesome, because most of it is awesome.