Stopped reading a couple times because of it's size, at 13.5 thousand pages, which also makes it hard to review. Being a work about twenty years in the making, such duration and consistency is bound to reveal both the author's personal evolution, as well as the reader's, considering I can remember watching the first episode on Toonami back in the mid '00s. It's hard to imagine that there are manga even longer than this, but there are, and usually the author's sole artistic work; I can't but think these authors are reincarnates of the authors of the old Indian epics, like the Mahabharata. Sure, Naruto is still a Shonen manga, 10+ year old boys, young adults, but the themes it presents are relevant even as an adult.
What it means to be a leader, the importance of friends, learning to cooperate with others -- these questions are explored here. If you're looking for some great bromances, they're here. Naruto and Sasuke, Kakashi and Guy...no yaoi, unfortunately, as that might have been able to pull in a larger female audience, and also unfortunately, that many of the female characters don't get proper development, and the ones that do are still usually support characters: literally, healers.
That said, what does get explored makes this series worth reading. It's rare for there to be a black and white character in the manga; everyone, even the monsters, if they don't have some humanity about them, do have something redemptive. The greatest schisms that result in this universe is from ignorance, a lack of understanding others, and oneself. Other reviewers have mentioned the Buddhist and Confucian elements here; everyone in this story is suffering in some way. Some commit terrible sins against friends, terrible crimes against villages or nations, and many of those that do are redeemed; the inevitable burden of karma falls against us relentlessly, yet, Naraka is not eternal. The cruelest scourge can be revisited at a later time, the blood on hands, and not bloody hands, washed away. A leader's role, knowing the weight of karma, of every action done by every living being, is to find a way of harmony through often discordant actions around him, and in himself. Bundles of movement, the world, Earth, being the largest and most relevant to us, appears impossible to understand, but this, as the ending of Naruto paints well, is the false choice of unity or division.
Naruto's admirable quest is to understand how unity in division is possible. We cannot, any one of us, return to unity without either dissolving in that unity or becoming that unity and trying to force others into it. The tragic individuality produced by division, separation from others, is precisely what can create, like in Obito, a hole that can never be filled, if one turns their back on others. But this hole in my heart, this emptiness, is also what others can fill if I'm willing to accept them. To be a lonely unity of individuality, an island unto myself, is a quest for power, of darkness, but not necessarily evil. To be for others, confident in myself that this is what I want, is to see the Sun in all living beings, while the power of deprivation is an individual's desire to return to a unified state.
The key then is understanding that one is being split apart in every interaction with others, but in this splitting is a chance of acceptance for others, the hope they will accept me, so that I can accept them into my heart. I am deprived of myself as I give myself to others, but with others I realize my vast power in being interconnected with all living beings. Emptiness, the source of deprivation and power.
Naruto is cool, you should read Naruto.