The ancient definition of epic poetry, a precedent set by Homer, is any verse of successive hexameters.  Virgil, in the Aeneid, uses dactylic hexameter, but Dante's poetry does not follow such a rubric.  It follows its own system of successive tercets where the last words of the first and third lines rhyme.  As we can see from the above left image of a manuscript of Dante, the tercet system is easily recognizable by every third line set apart somehow.

Structure
Dante's Divine Comedy is a highly structured work - his verses fall into a kind of hierarchy that any order-obsessed Roman would have loved.  Again inheriting from Homer, Virgil's epic poem is divided into twelve units called books, each book a self-contained unit.  Dante takes that level of order even further - so much so that his work is almost perfectly symmetrical.  The comedy is divided into 3 canticles of 33 canti each, with one introductory canto.  Important episodes within the canti take place at midpoints in the canticle, making it clear that Dante did all this symmetry on purpose.  In addition, the structured nature of hell, Purgatory, and heaven further reinforce the hierarchy in Dante's writing.
 

Dante's Death Mask

Language Most high school English courses teach that the significance of Dante's Divine Comedy was that it was written in the vernacular, or the commonly-spoken language of the times.  Dante broke from tradition when he wrote such a major undertaking in Italian, for Latin had for years been the preferred language of the educated elite in his society.  In doing so, he made his writing accessible to everyone - not just a select few.  In a way, this decision was an intellegent one, given the subject matter of the Comedy.  If the purpose of his canticles was to teach Catholic doctrine and theology in the hopes of spreading his religion and eliminating sin, Dante was wise to make his work readable by the very people he was hoping to save from damnation.

Virgil, although his classical Latin was the vernacular of Rome, achieved a similar goal.  The Aeneid was a book accessible to the masses not only because of its readability, but also because of its subject matter.  What Roman citizen didn't want to hear about his country's glorious past?  The story of Aeneas and his men pulled at the patriotic heartstrings of the masses.  In addition, Virgil masterfully tied in the folklore of the age, too.  The Aeneid makes numerous allusions to mythology that every Roman knew - their myths were their "pop culture" - and thereby increases its popularity even more.