The Series Naruto, not the character.
Why has Naruto become less interesting?
Do you remember few years ago when you first started watching/reading this series and you were so excited about it that you stayed up till 5 am to catch up on the rest of the episodes? At that time, I thought, "WOW This is the best anime ever!" Don't get me wrong, Naruto is still a good anime/manga, just not as great as before. In this post, I'll try to list out my view as to why it became less interesting.
Music. Yes, music makes a huge difference. Music alone will stir up a person's emotions if the music is powerful enough. The heavy rock music that came on when characters in Naruto were getting pumped that pumped you up as well; The sad flute/instrumental song that came on when you thought one of the characters almost died; Heck, even the opening/ending song itself was awesome. Naruto used to use great Artists like Asian Kung Fu Generation but the music from Shippudan seems totally different from the music in the original series.
Storyline Progression. People might disagree with me on this part but I feel like the length of this show really killed it. As a manga reader, every week, you wait for new chapters to receive mere 14 pages of Naruto. Some of those chapters hardly developed through the storyline and some were completely waste of pages (everytime I saw Konohamaru's face, I panicked for pages) As an anime viewer, a lot of the fights dragged on. People stood still staring at each other for a while, saying the obvious lines and wasting time. (For example, remember how long it took for Kakashi to use his newly found MS? In the manga, it felt like a 5 second delay. In the anime, the delay was like 20 minutes?) To make things worse for the anime viewers, they got hit with 2 waves of Filler seasons. We all know fillers are bad but some were so bad that you were constantly wondering who the ^%#@$ wrote the fillers. In my opinion, it would have been better to use those filler episodes as Naruto humor episodes where Naruto goes around Konoha and interacts with each character to create humor and character development rather than horrible action scenes and lame bad guys with bad stories.
Repetition. When the show started, I had great expectations. Because a whole new wave of techniques and concepts were introduced to us viewers, we felt like we could take those concepts and expand on them for more unique styles of combat. But what we received was constant repetition of the same stuff. Same fighting style, same fighting techniques. When Naruto first learned how to make a Rasengan, I was thinking, "Wow, I hope he learns some support jutsus with that!" But instead, he makes a bigger rasengan, rainbow rasengan, etc. You know that the writer is getting lazy when you see Kakashi, who is supposed to know 1000 jutsus, only use 1 jutsu (Chidori) over and over again.
When I first watched the Zabuza arc, I was so moved by the anime. It was emotionally and action packed. It made me think that the show had so much potential to expand further. After the Chunnin Exams, the storyline seemed to move into something so predictable and un-unique. Fight that all-powerful evil group with our main character as the hero. The main character must start out weak and then gradually become stronger to beat the evil bad guy, etc story. I felt like Naruto emphasized too much on which characters were good (Konoha, Naruto) and which characters were evil (Akatsuki, Orochimaru) It would have been much more interesting to have the main character do something out of the ordinary.
Character development has been a big issue as well. The character who we all know to be in dire need of major character development, in terms of both power and mentality, is Naruto himself. A main character is a very important character because that character is directly connected to the reader. Throughout the characters in the show, you are initially biased in favor of the main character compared to the other characters because it is the main character. If you have a horrible main character, it makes people not want to watch the show. Naruto is not horrible main character, but in my opinion, he can do much better. After all those years watching this show, Naruto has barely changed in mental attitude. Even my real life little cousin has gotten more character development during the lifetime of the show than we can ever wish Naruto for.
Perhaps the fact that Naruto has been around so long, makes us painfully aware that every jutsu, story, character is something similiar to what we've already seen. I have to admit, Naruto has been going for a very long time. But maybe thats also rewarding because we have a community of readers who can discuss each chapter instead of a finished series and having no person to analyze each event about.
Maybe I wasted 10 minutes of your life but if you spent the past few years watching Naruto, you should really think about how much the show has changed.