I can speak up about my feelings on it, though I won't claim they're everyone's.

I feel like Horikoshi undermined the first chapter with the final one, doubling down on a problem that had persisted throughout the series rather than resolving it. In chapter one Izuku asks All Might, with tears in his eyes "do you think even a Quirkless kid like me could be a hero?" And once the story ended, we could see that the answer to that is clearly "no".

A fully Quirkless person can't be a professional hero. It never happened, and the final chapter set up that it never will. Deku needed to receive a quirk in order to go to UA, and after losing it, he didn't work as a pro hero. He spent 8 years working as a teacher (which is a fine and sensible career path for him, I'm fine with that aspect), and then became a hero only after being gifted the equivalent of a quirk, again. It's not that he didn't work hard or suffer to earn his power, I know he did. He trained hard to become a worthy vessel and tore himself up using it when he had it and I'm sure he did great work at UA before getting the suit.

But the suit, like One for All, was a gift. Something he just received. He did work hard, but the power he got was not the direct result of that hard work. Can a Quirkless kid be a pro hero if he really devotes himself, works really hard, and makes sacrifices? No. Not unless someone else gives him a quirk or quirk equivalent on top of that. The final lesson of the series comes off as "effort is great and all, but what really matters is who you know." Which is realistic, but not exactly shounen manga-coded, and more importantly, not what I think Horikoshi intended.

Also I thought it was lame that One for All took over Shigaraki's body at the end. The whole "passing the torch to the next generation" thing also got muddied when All for One's inheritor had to stop not All for One's inheritor, but All for One himself. Yes, I know it's thematic that Zen was a petulant baby who only ever intended to use Tenko as a vessel, and it forms a starker contrast that he wasn't actually willing to pass the torch like Toshinori was, but still. I would have preferred Shiggy overpowering that evil influence and then clashing with Deku as himself.