It's 2020, can we stop pretending that Mario 64 is the magnum opus of 3D Mario?
I tried to play Super Mario 64 seriously for the first time before Super Mario Odyssey came out, since I'd played Sunshine and Galaxy pretty thoroughly but never 64, and while it was certainly fun and does hold up in a lot of ways... It was just a bit too simplistic for my tastes. Compared to how much personality and creativity are bursting forth from Sunshine, Galaxy, and later Odyssey, Super Mario 64 felt rather basic in its overall design. Makes sense, obviously, for the progenitor of all 3D platforming, but it didn't grab me by the collar as the best game of all time.
It's one of those things where, at the time, a game is incredible, it was a landmark achievement for the genre or industry, and it still holds up and is fun today, but newer players going back and playing it fresh might not find the same enthusiasm about it as those that grew up with it.
Another example for me is when I tried to play Morrowind after hearing certain fanboys praise it as the best Elder Scrolls game and trash talk Skyrim and sometimes Oblivion, so I went and played it, and... yikes, that game is rough if you aren't very familiar with its quirks or how games like that were back then.
Same thing with Super Metroid for me. I'm a big Metroid fan, but I only really play the Prime games. Last year, I went through and decided to play all the 2D ones I hadn't played: Zero Mission, Super Metroid, and Fusion, in that order. I thought Super Metroid was good, but I've seen some people literally say "Super Metroid is the best game ever made, period," and that was not what I felt while playing it. It certainly holds up, but there's a lot of things about it that I think are antiquated and have been improved upon by Metroidvanias that came after it. I definitely still prefer the Prime games.
I think about that kind of thing a lot with my favorite games. They're all my favorites because I played them when they were fairly new, but someone going back and playing them for the first time 15 years later won't get the same effect. They'll have played games of that genre that have refined and modernized some elements, and they might be put off by some of the old-fashioned details in these games from long ago.
The only exception to that kind of thing in my case, I think, is Castlevania: Symphony of the Night. I've beaten that game about a dozen times, two of them being 200.6% runs, and it's always a joy to come back to. I played it for the first time in 2011, 14 years after it was released. Nothing about it felt outdated to me, and I don't know what anyone else could say that might be offputting about it in the present. That game is pretty much as timeless as it gets (though the voice acting and writing are certainly dated--but in a charming way).