I was moved to see is because I know a bit about the Mahabarata - we saw the Indian TV version many years ago (it ran weekly, for quite a few months).
The first surprise was the intermission, after only an hour!
I don't know how involved the Disney company was in it. The character animation reminds me a bit of Disney's "Pocahontas", but the overall animation is unsurpassed. In one or two places, actual scenery is combined with the animation - but it is so well done you have to look for it.
I think someone would enjoy this movie even if he didn't know the Mahabarata - but it certainly helps. The story glosses over some important details: why is blind King Dhritarashtra's wife blindfolded? Who is this Krishna fellow? And why is Arjuna disguised as a woman?
There are at least two scenes that I remember from from the epic that are in the movie: one when Arjuna is learning archery from Bhishma [?], and sees only the eye of the bird in the tree (now we know he's going to be a great archer); the other when Yudhishthira loses his shirt in a dice game, run by the treacherous Shakuni. There may be others.
The movie is a slice of the Mahabarata: it's Arjuna's story, how he grows into a true prince despite the best (=worst) efforts of the Kuru.
Even if the story on the screen is hard to follow, the animation is superb. I have not seen better, even from Miyazaki. This is one movie I could see again.