I don't know if this is a great reason but here goes the simplest version of the truth: it makes me smile when I watch it. It makes me laugh. It makes me cry.
I can relate to the characters and I have grown to love them and anticipate reading more about them every week - it's a constant part of my life.
Naruto strikes a chord with me like very few animes do. It challenges my imagination. It touches me, it teaches me, it changes me.
All in all: Naruto is the perfect example of a timeless piece of art/literature that reaches people regardless of status, race, believes, culture or ideology. Is there a way not to love it?