For me, even naruto change looks because of his kuubi. I feel like his power never change at all. Well, i guess only in speed and his rasengan got much bigger. but if he is really gotten stronger than the other, why would sasuke and other kages can much him? If the kyuubis power is really that strong why the other shinobi can much him? Thats why i felt that he didnt much change at all when it comes to power, just in the appearance.
With full and free access to his Kyuubi chakra, he has a ridicilously huge amount of chakra available to him, to such a degree that even after creating a ton of shadow clones while in Kyuubi form, just
one of those clones alone were still able to pull off a Rankaiten (violently spiraling) Rasengan, Rasen Shuriken, and an attempt at a Bijuu Bomb, before running out of enough chakra to dispel the Kyuubi cloak. He held his own against the third Raikage. All of that, with just a shadow clone! And then said shadow clone finished off by using Sage Mode and a Rasengan to defeat the third Raikage.
That's one thing. Next, his cloak allows him to sense not only chakra like other sensory-type ninja can do, he can even sense "evil intent", which no-one else currently alive can do. So nobody can hide from him. Then there's the fact that he's now the fastest ninja alive, possibly along with Ay (the fourth Raikage), making him the second-fastest shinobi in history (after Minato, which I think was still a bit faster than he currently is...Maybe...). He also has the ability to extend his Kyuubi chakra into arms, which together with his speed means he's a monster at Taijutsu. He can also use his Kyuubi chakra arms to create multiple Rasengans (Rasen Rangan), a massive Rasengan, or theoretically, even multiple Rasen Shurikens (remember he used two tiny Kyuubi chakra arms on his finger to make a mini-Rasen Shuriken). And let's not forget the Bijuu Bomb of course, a seriously powerful attack. And all of this comes in addition to what he already had: Sage Mode, Summoning Jutsu, Tajuu Kage Bunshin, all his older Rasengan attacks, and Frog Fu. And his ability to heal wounds quickly due to the Kyuubi.
In terms of both power and offense, speed and agility, stamina, sensory, ninjutsu and taijutsu, Naruto is top-notch. The only areas where he is lacking are defense (although he does have his fast healing ability) and genjutsu. However, the Nine-Tails can wake Naruto up from genjutsu thrown at him in the same way that the Eight-Tails did with Bee in his fight against Sasuke (and that was against a genjutsu cast by a Mangekyou Sharingan no less!). So basically genjutsu are useless against him, and he'd beat most people in a test of taijutsu because of his speed and his Kyuubi chakra mode arms (though the third and fourth Raikage has him beat. I'm also not sure how he'd fare against Gai with 7 gates open...). So the best bet to beat him is to best him with ninjutsu, but Naruto's own ninjutsu are very powerful.
P.S: Not criticising you or trying to be mean here, but I'm not sure what you mean by "can much him". That doesn't work in English. Just thought I'd point that out. I'm guessing you're trying to ask why Sasuke and the kages would be able to beat/defeat/best him (Naruto)? And the reason Sasuke could potentially match Naruto in a fight is simple: Susano'o+Amaterasu. Ultimate, impenetrable defense, and instant deadly attacks. Though I'd like to think that Naruto would use his speed and sensory abilities to avoid all of Sasuke's attacks, and then just use his crazy stamina and huge chakra capacity to simply outlast sasuke, and wear him down until he can't keep his Susano'o up any longer.
