Donnelly considered "Octavarium" to be "somewhere between "Images and Words", "Six Degrees of Inner Turbulence" and "Train of Thought"". Carlson stated that the album "draws closest comparison to "Falling into Infinity" and "", but with far less complexity and edge." Tammy La Gorce of AllMusic noted that "a post-hardcore edge - call it a leap into 2005 - has invaded band's pledge of allegiance to theatrical heavy rock... What's changed is Dream Theater's commitment to carrying on their reputation as underground progressive rock's classicists, and it seems well-timed." Critics noted a strong Muse influence on some tracks, on some cases generating negative reviews.