Usually in threads like this people tend to offer little more than meaningless platitudes that can be applied to most characters in the same genre. Naruto's a fighting genius, is he? Well, how unique. He's as special as Goku, Luffy, Ichigo, Gon, and just about every other shōnen hero worth mentioning.
Nope. Platitudes tend to offer nothing of real value in discussion. In fact, I'd go as far as to say they prevent actual debate. Anyway, moving on to the point.
Naruto is an incredibly dangerous individual. Not because he has a bijū, not because of his Sage Mode or lineage, but because of two particularly dangerous attributes that make him a force to be reckoned with. Those attributes being that he fights without consideration for his own safety and has no predictable pattern. Just look at his fight against Kakuzu. He put himself at such a risk, not even an experienced shinobi like Kakuzu, who was undoubtedly superior at the time, could have predicted it. Naruto always keeps his opponents guessing and he always manages to trick them into guessing wrong. He's done it Zabuza, and he's done with Neji, Gaara, Nagato, Obito and pretty much everyone he has every fought. The more his opponents try to predict his moves, the harder it becomes for them to get a fix on him.
Aside from these two attributes, Naruto learns by doing. He's not an intellectual and he's quite ignorant, but he's not an idiot. If things are put in terms he identifies with he'll understand. See Gamakichi's explanation of how Senjutsu works using ice cream. Your first instinct is to write Naruto off as an idiot, an imbecile who is hardly capable of critical thought. The thing is, Naruto is an idiot without actually being an idiot. He's slow on the take, sure, when it comes to things he doesn't particularly care for like information on things he doesn't mess with often, but once he's interested, he absorbs the subject mater and masters it, e.g. like he did with Senjutsu.
Naruto would be no less dangerous without his bijū. It's the man under the armour that counts.
