Shippuden has 204 filler episodes. At a certain point it becomes a chore to finish it and you're better off reading the manga. But I guess if you really love the franchise then it won't matter much.
The initial hook of Naruto is that you're following a talentless underdog with no friends, no family who has to prove to everyone that he has value in the world. But in Shippuden you learn that he's actually privileged as hell and more or less destined to become a top ninja if not Hokage someday. This undercuts the foundation that the original anime was built upon and is a flaw in the narrative.
The villians in Shippuden are 10x's more threatening and so many likeable characters get fukked up. This makes the battles feel like they have more weight to them, because you can't be sure who will survive in the end except for a handful. This was an upgrade from the first season.
Naruto does a better job of making every character feel like they matter. Shippuden puts fan favorites on the backburner to overcook the Sasuke/Naruto romance/rivalry that becomes hard to believe at a certain point. Naruto literally getting on his knees begging for this man to return to the leaf village, at one point even hyperventilating because this stresses him so much (???), never really felt as convincing as the show tries to make it look. Not as much as it would've if they were still children.
The music is the most memorable part of the Shippuden experience to me. Some of the songs drove the scenes as much as anything happening in them actually do, some of the OP's and ED's send me on instant nostalgia trips.
same score as Naruto, 6. Does some stuff better, other stuff worse, still a lot of filler, really hurt by HxH 2011 and FMAB showing what an ideal adaptation looks like. doesn't do anything that some shounen before it didn't do better like Yu Yu Hakusho which I bring up in every thread because it's great.
I guess "The Last" movie doesn't count in this, but the ending scene from that was so good. Brought everything around full circle with the entire village there to celebrate Naruto and Hinata's marriage.