Scholars, saints, ascetics, enthusiasts, literature experts... they all have different views of how to classify Mahabharata. Though, the consensus is that it is the longest poetry ever written. 

Mahabharata itself classifies it as: Arthasästramidam proktam dharmasästramidammahat Kämasästramidam proktam vyäsenämitabuddhinä.

It's a treatise on economics, morals and duties, love and seduction, and also the guide to peace and salvation. It declares, that what is found here can be found in many other places too, but what is not found here, that cannot be found elsewhere. 

Yadihästi tadanyatra yannehästi na tadkvacit. 

That's a bold claim. I don't find drone making instructions in there. However, I realize, it is classified as 'Itihaas'. Often, that gets translated as 'History'. Though that is akin to mistaking the political liberal faction as being flexible or opposite of obstinate or the political conservatives as the keepers and protectors of virtues. In that light, I find how to make forts, houses, fields, weapons, food and even decorate hair. Oh, and how to make love too.

Itihaas is manner of narration, in multiple layers. There is this layer of events that gets mistaken for the equivalence of history. But that's a small, and central, component of it. Literally translated, itihaas means, 'And thus it happened'. It is a way of explaining the destiny one has found self in. And therein, the claim of 'what is not found here, that cannot be found elsewhere' comes into picture. The epic claims to have documented everything that existed in that period. Art, Science, Philosophy, Erotica, Architecture, Music, Astronomy... et al.

This style of narration is prone to subjectivity and inconsistency even if one gets pedantic. The sequence of core events remain the same, but the explanations and details of the layers vary by the narrator's own depth of understanding of the world. This 'flaw' makes it a discipline that flows amongst seekers and in a civilized collaboration. This style can't survive violent scrutiny. 

In itihaas, all these streams of knowledge are weaved into the narrative of the sequence of the events into multiple layers. They are connected and yet intelligible on their own. Vyadha Gita (in Van Parva) stands as a philosophical text on its own and yet it is part of the overall epic. Same with the dialog between Draupadi and Satyakama (also in Van Parva) which has been a baseline for the text of 'Home Science' textbooks in schools as recently as 30 years ago. (Although it is now a politically incorrect and even regressive set of text.) 

One of the most common mistake people make is to interpret it as a book of war. Or a glorification of violence and power in some sort. Nothing could be farther from truth. Mahabharata is a book of peace, narrated to prevent conflicts and eventually, establish peace and harmony. But to understand that, one needs to open the book and read the beginning of it. 

Arjuna had killed (set aflame) several tribes to setup his kingdom. One of the surviving victims resolved to avenge it and killed Arjuna's grandson. Enraged by this, Arjuna's great grandson sets forth on a mission to unleash hell's fury on the tribe of the killer. 

Mahabharata is the tale that successfully prevents the repetition of the violent cycle that would have created more victims and caused more miseries.  

The kind of importance we ascribe to the characters in Mahabharata and the scale we imagine will make it difficult to believe that tale of Arjuna and Krishna, Yuddhisthira and Bhishma was nearly forgotten even before the fourth generation. We can safely say that the narration of the tale in form of Mahabharata has ensured that it survived more than 4000 years now. 

With all its reference to Dharma and religiosity, it is not a sermon. Chapter after chapter, it documents the events in light of decisions taken in certain circumstances. The cycle of time and the consequent impact of events cannot be avoided, even by the Lords and the gods, the Kings and warriors. 

The narration of Mahabharata concludes, to paraphrase, those who listen to the tale in entirety will be able to end their internal conflicts, even if struggling with the guilt of grievous crimes and will be able to see themselves and the world around them in a more benevolent light.