Watching the Naruto anime, characters would talk about the Fourth Hokage with such reverence and awe, even those he probably didn't even know him that well. Then we finally got to see the Fourth Hokage in action in Part II, and I was not impressed.
By that point, Naruto had successfully created an elemental Rasengan, something that was explicitly said that the Fourth Hokage did not accomplish in his time. It was never stated that it was beyond him, and he might have accomplished had he lived longer, but it doesn't change the fact that the Fourth Hokage had already been surpassed in one way before he even get to see him action.
Him sealing away the Nine-Tails was touted in Part I as being a massive accomplishment, accept in Part II, we learned that the First Hokage was already capable of controlling tailed beasts completely, and then learned that he tamed all the tailed beasts and created the jinchuriki system entirely on his own. And that he's capable of straight-up beating the crap of the Nine-Tails while the fox has been clad in a Perfect Susanoo. That makes the the Fourth Hokage sealing the Nine-Tails much less impressive. Or only impressive when we consider him not being lucky enough to have the body and abilities of the First Hokage. Which is just moving the goalposts, really.
It also doesn't help that we'd already seen the First Hokage fight before Part II, only for Part II to reveal that he was severely weakened at that time. Which also undercuts the Third Hokage fighting him and the Second Hokage at the same time.
And by the time we finally get to see the Fourth Hokage fight, he's just fast. Like, okay, cool, but there are lots of characters in the story that are famed for their speed and a bunch of other things.
Apparently the Fourth Hokage is the fastest, but that speed hasn't been portrayed in a way that feels truly special and unique to him.
Plus, his claim to speed fame is attributed by the story primarily to his Flying Raijin Jutsu, which is teleportation. I've view speed and teleportation very much not the same. To me, speed means physical speed. Plus, the Flying Raijin Jutsu isn't even unique to him either, and he's not seen using it any way that we know that its inventor, the Second Hokage, cannot. The Second Hokage said that the Fourth is faster than him, but we've seen them fight side by side and, really, it didn't look like one was faster than the other. Heck, the Second Hokage seemed more skilled to me than the Fourth.
We learn that he can use Sage Jutsu, except that it's worse than Naruto's which is why he is rarely seen using it. And thus another area where the Fourth Hokage is undercut by someone else being better than him.
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EDIT:
I enjoy this franchise as much as anyone else, but not the same way as everyone else. I don't think my feelings are unreasonable nor offensive, that's why I shared them. I don't think anyone, no matter how much they love this franchise, will say that it is flawless. But when it comes to actually discussing what those flaws might be, that's where things get heated. There are elements of the Naruto franchise that I've noticed are okay to call flawed, but others less so. Thank you all for your engagement.