That vintage aesthetic Harry Potter gives off in both the books and the films is definitely top notch and no doubt a big reason why so many people give so much of a shit about it despite all the many flaws.
It absolutely is a big reason why, especially for kids in the US because, speaking as part of that age group, we had never really seen anything like Harry Potter's retro flavored English culture before and it blew our minds, it's the same exact reason that meanwhile Pokemon, DBZ and Sailor Moon were blowing up with kids at the same time.
If you were a kid in the 1990s for most of the decade you grew up in a very American centric culture, Nickelodeon, Disney movies, Goosebumps, Cartoon Network, TMNT, Batman TAS, Superman TAS, the 90s Spider-Man cartoon, the 90s X-Men cartoon and so on.
All of that was cool, sure, but then at the end of the decade along comes our first real explore to foreign cultures and it blew our minds because we had simply never seen anything like it before.
Now in the case of Japan there's a few exceptions, there was Nintendo, Power Rangers and the whole "ninja" craze (ala TMNT) all of which was popular earlier than the late 90s, but in the case of Nintendo and Power Rangers they played it coy with their Japanese origins, as a kid I knew Nintendo games were from Japan, but I didn't know much about Japan itself and nothing in say Super Mario Bros was real Japanese culture specific (or least references we could possibly have gotten at the time, like the "Tanooki suit") and probably a lot of kids didn't know, in the case of Power Rangers kids definitely didn't know since they reshot scenes with American actors, I certainly didn't know Power Rangers was originally Japan.
And as for the "ninja" craze with stuff like TMNT, that struck a little older, kids who went nuts for Harry Potter, Pokemon and Toonami tended to be kids born in the late 80s, the "ninja craze" and TMNT tended to be more for kids born earlier in the 80s, either way they had never been quite as strong an exposure to Japanese culture to American kids until Pokemon/Toonami in the late 90s and certainly nothing like Harry Potter until the late 1990s.
What's funny is the British/Japanese thing seems to have created a schism in millennials, speaking personally I had some exposure to Potter, saw the first two movies, played the PS1 game, even bought one of the toys (the potion maker thingy) but never found it interesting enough to actually sit and read the books, I was more drawn to the Japan side of things ala Pokemon and Toonami, for me the cute girls of anime drew my attention more than the dorky kid with the glasses named Harry Potter, I assume boys were more drawn to stuff like DBZ and girls more drawn to Harry Potter precisely because they found that dork cute.
As time went on this basically lead to "weaboos" and "teaboos" and again I think the former tended to be more males and the latter more females, the "teaboos" later got into stuff like Doctor Who, Sherlock, Black Mirror etc, us male "weaboos" got into more and more adult anime/manga (sometimes REALLY adult anime/manga) and eventually it blossomed into a political schism with "teaboos" tending to be SJWs and "weaboos" tending to be more anti-SJWs, this has culminated in SJW "teaboos" declaring jihad on the person that made them love British culture in the first place, JK Rowling and support politics that ensure British culture will one day go extinct as fuck, the irony.
Speaking personally again I definitely have an interest in British culture too but I lean more in the direction of stuff like Pink Floyd, Queen, The Who, Led Zeppelin, later bands like Blur and the Gorillaz or even stuff like Thunderbirds (the original puppet show one) or Garth Marenghi than stuff like Doctor Who or Harry Potter.
