The Mahabharata itself says it quite positively.

 What is found herein may also be found in other sources,
     What is not found herein does not matter.
The Mahabharata contains virtually all the lore and legend of the Classical Hindu Tradition - which is also, in typical Hindu defiance of simple-minded historicity - very much a living tradition. Here are the great creation stories - Manu's flood, the churning of the milk ocean, the descent of the Ganges. Here are the favorite myths and fairy tales. Here are the jokes. Here are the codes of law - moral, ethical, natural. One of the best things about the Mahabharata is its wonderful richness of episode and detail.
But Mahabharata is not a random collection of tales, like the Medieval gestes (to further prove the habit of thinking Eurocentrically). Every digressive bit of the Mahabharata is there to shed light on a central story. The core event of that story is the great battle that was fought on the field of Kurukshetra between the five sons of King Pandu and their allies on the one side and the hundred sons of King Dhritarashtra, with their allies, on the other side. The battle was the culmination of a long history of struggle and diplomatic maneuvering, and it involved virtually every tribal king and every powerful city-state in Central and Northern India at the time.
It was a tragic war, that pitted brothers against brothers, sons against fathers and uncles, brave noble men against brave noble men. And it was devastating. Nearly all of the best men died in the long battle. The Pandavas, the sons of King Pandu, survived, but there was no victory, for the war had destroyed the world that they knew, and the emptiness of what they had won colored the rest of their lives.
Now to say that the Mahabharata is the story of a great battle is to say that Hamlet is the story of an unsuccessful usurpation, or that Moby Dick is the story of a whale hunt. Hindu cosmology is sweeping, and the story of the Mahabharata war has cosmological significance, in that it marks the end of one yuga and the beginning of another. There are four yugas in every great cycle of existence, each one diminished from the one before. The yuga that ended with the Mahabharata war was the dvapara yuga - the age of heros, during which noble values still prevailed and men remained faithful to the principles and tasks of their castes. The age that follows the battle is the Kali yuga, the last age of the world; in it, all values are reduced, law becomes fragmented and powerless, and evil gains sway. We live in the Kali yuga.
The breadth of its vision is one of the things that makes the Mahabharata the best story I know. But there are other reasons. Mahabharata has a riveting plot and a compelling dramatic structure. Its characters are complex and real, with depth of personality that is unmatched in any other epical or biblical story I have heard. Finally, I have found the Mahabharata to be full of wisdom.
In the next few minutes, I am going to try to give you a sense of how the Mahabharata story goes.
Since the story has cosmic significance, its ultimate beginnings are lost in the mists of time and the minds of unknowable immensities; a wealth of family histories, myths, and fables lead up to the events that I will tell you about. I will jump into the story at a point where the succession to the kingship had come into question.