When asked about an incident where another famous horror writer was accused of ripping off his ideas, Stephen King simply brushed it off. He said that he had no problem with someone creating a story with similar themes and ideas. He compared it to having an apple and a pear—both equally delicious, sweet, and juicy, yet distinct in their flavor and composition. It is true that Kamatani, the mangaka, is a huge Naruto fan-girl and looks up to Kishimoto as a role model. However, her work isn't meant to copy nor is meant to compete with Naruto. Nabari is paying tribute to Kishimoto and Kawajiri (Ninja Scroll) in the same manner that Naruto pays tribute to Katsuhiro Otomo (Akira) and Akira Toriyama (Dragon Ball). This is a very common aspect of Japanese culture, since those who come after always want to respect those who have come before. I think those who are comparing Naruto and Nabari and those who insist that there are no similarities ought to keep this in mind. They are similar in themes and ideas, but also are quite distinct. They both have their strong and weak points. So why should we sit here and say one is necessarily better than the other? As a fan of both Naruto and Nabari, I certainly won't. What I think is helpful is to compare and contrast the two series.
I think that anyone who likes Naruto will most likely enjoy Nabari. The mysterious inner demons, unique style of shinobi, interesting adventures, twists, crazy sensei, and tragic back-stories will undoubtedly be familiar. Yet, the abundance of differences that you find in the world of Nabari will pique your interest and keep you hooked. The settings in which the stories take place are quite different. In Naruto, you have an alternate world with what seems like a weird mix of Edo-period, Meiji-period, and present day settings and technologies, most of which give it a more historic than modern flavor. However, Nabari is firmly set in present-day Japanese society, with all its conveniences and conventions. In Naruto, you don't see things like automobiles and firearms, but these are as fundamental to the world of Nabari as shuriken and kunai. I believe it must have been a real challenge to do this, especially when ninja and samurai are obsolete in a modern world of highly skilled snipers and mercenaries. However, Nabari manages to pull it off and the result is a complex setting that is both interesting and eminently believable, despite the occasional over-the-top incidents (ninjutsu presentation at a science fair?!?).
The main character of Nabari, Miharu, has a very different personality from that of Naruto. Ah, how to say, the word apathetic does not do it justice. Rather than merely being “window dressing,” Miharu's reluctance seems to be more of a way to defend himself from further hurt caused by emotional attachment. The indifference is nothing more than a façade; the reality is that he cares more than he lets on. In fact, despite the shell Miharu erects around himself, he comes to have a core set of “important” people whom he is willing to go to great lengths to protect. He also finds himself inextricably linked to one character particular, Yoite, who he wants desperately, above anything else, to save from the darkness and self-destruction. It may seem that he is similar to Naruto because of these latter aspects, but, unlike Naruto, he doesn't wear his heart on his sleeve. They both share tragic, parent-less pasts due to their inner demons, but Miharu receives far more support earlier on while Naruto is left to on his own. I think this key difference reflects an important theme shared between the series. The kanji for “nin” in the word “ninja” has the main meanings “endure” or “bear.” It is because Miharu has the support early on that he strives not to burden others with his problems. Miharu's quiet and reserved way of enduring is just as compelling as Naruto's, but connects the reader to Miharu in an entirely different way. Miharu is quite perceptive and is anything but naïve, thus his approach to problems stands in stark contrast to Naruto's more emotional and direct approach. Also, Kamatani really likes to use Miharu's harmless emotional manipulation as a source of comic relief. Sometimes this can be quite distracting and over-the-top, but it is a trait that also makes Miharu likeable in his own way. Like others have said, the intensity of some of his true feelings really is borderline shounen-ai. In many ways, the Miharu/Yoite relationship mirrors that of Naruto/Sasuke, but in many ways it does not. This is mostly due to the fact that Yoite lacks the same inferiority complex and is far more consigned to what he feels is his own self-destruction. Also of importance is the fact that Yoite is introduced from the start as a serious enemy of Miharu, so the amount of time they actually spend together is quite brief. Yet, in spite of this, strong bonds and connections are built. As for the other supporting characters, their development and stories are also compelling. You have the foreign teacher, Thobari, whose connection with Miharu is quite complex. His eccentricity is sometimes interesting, but at other times it is just stupid. Also, there is female samurai, Shimizu, whose tragic past—involving her older brother's murderous betrayal of the clan—seems to mirror that of Sasuke from Naruto. Yet, she could not possibly be more different. She is headstrong, hot-blooded, emotional, and even quite noisy at times. She seems quite set on taking revenge on her brother at all costs, which is not unlike the primary motives of Sasuke. Usually, I simply detest bimbetts and moes, but there is something about Shimizu that makes her quite likable. Shimizu's brother is also interesting, but seems quite similar to Itachi from Naruto when you learn more of his past.
The art is decent, though the super deformation gets annoying at times. As for action, there is enough to keep to series interesting, but clearly it does not play as much of a role as it does in Naruto. The slice-of-life theme tends to get more face-time in this series. Also, contrary to what some have said, the characters still call out their techniques, so you can expect that along with technique explanations during battle. The story tends to get somewhat stuck at times, but I feel that could be due to the poor quality of some of the scans as well as the disjoint manner in which they are released. Nonetheless, you can still expect an emotional roller coaster, as there are times where you really feel your heart being tugged at. If there is any negative aspects, it is that important details are not explained thoroughly and end up falling through the cracks while trivial ones are sometimes given too much weight. Unlike Naruto, it was planned to be a short series, so perhaps the level of detail was restricted by necessity. I think the are both good and bad aspects to being a planned short series with a definitive end. I do not agree that being a short series necessarily makes it superior to the longer, open-ended series. Still, I definitely think that is one of the better manga out there and well worth the time I invested into reading it.