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I mean, that's all there, but I really think you could pick up on a lot of these things if you're a late joiner. A lot of things, such as the relationships between characters, reanimations, and the curse mark really seem like things that would be reinforced if I'd read the original, but I don't think I'd feel lost if I hadn't watched it. A lot of things are reintroduced and developed in Shippuden, so it makes them easy to latch onto. Even the worldbuilding is pretty simple in Naruto, enough that you could watch Shippuden and clasp onto how things work.
And I really do think that, to get behind the characters, you do need to invest in the original Naruto. But I think it's because Naruto is so much more simple compared to Shippuden where things are reintroduced and developed (and I really think it's because a lot of things start developing complexity here rather that it works), that it's not a necessity for a prospective fan.
And I don't mean it like that, I mean something you could put on a bookback description. The original was always basically "Enter Naruto, a hyperactive delinquent ninja that wants to be hokage! Follow him and his friends, Sakura and Sasuke, as they head forth on their quest to become world-class ninja". Until Orochimaru entered, of course. Then things got focused.
Eh...the thought was a lot clearer and more developed in my head when I thought it. I said "the other day", but this was actually a few weeks ago.