All right, Lee, I'll give it a shot.
First things first, I do love the Mario series and the original Super Mario Bros. in particular. I regularly play through it every few months. The old-school graphics are gorgeous in their own way, with a sense of style that only an old-school game can evoke. The pick-up-and-play formula is balanced with incredibly challenging levels full of warp pipes and hidden beanstalks galore. The music is as memorable and catchy as the day it was produced. It saved the gaming industry from extinction...
...But it's not a better game.
Innovation and fun can only get one so far. When I play a video game I want something that can capture my imagination, that I can go to again and again and get something new out of it with each playthrough. I want something that can make me feel a variety of emotions while still being a blast to play. While Super Mario Bros. is definitely something I can play often, it really doesn't change with each playthrough. Once you've found all the secrets, it's really just a game about jumping around on Goombas and Koopa Troopas. I've memorized it enough to know the secrets and blast through it without batting an eye.
Majora's Mask, I have said again and again, is an experience. Every time I play Majora's Mask I find out something new. I'm not just talking about easter eggs or hidden areas, but little lines of dialogue that I didn't notice before, or thoughts that I didn't have the previous time I played it. It's really tough to verbalize exactly the feelings I get when I play the game - It just has that magical "It Factor", comparable to when you're listening to an incredible piece of music or watching a wrestling moment that you just know will live on forever.
Majora's Mask's graphics are just as interesting and sharp as when they first came out. They've aged similarly to Super Mario Bros. in that regard, with grace and charm. The environments are just as atmospheric as when they were first shown to the world, just as eerie, and the moon is just as ominous. The music in the game is just as catchy as classic Super Mario Bros. tunes - Fitting, considering the same composer did both.
The gameplay is still top-notch. You say that Mario can be picked up and played? So can Majora's Mask. It's not hard to press a button and shoot a bubble or slash a sword. Each new transformation feels familiar yet different, intuitive and fun. The world design is intricate and deep, yet easy to navigate and fight through and explore. Majora's Mask also has more varied gameplay than Mario, with stealth sections, swimming, shooting, and more along with the base adventure gameplay. Mario has swimming sections, and it has platforming sections. And while the levels are large and interesting in their own rights, it can get a bit repetitive when played for a long time. Majora's Mask has variety and sidequests galore to keep the game fresh and fun.
There are very few games I would call brilliant. For me to call a game "brilliant" it needs to have longevity, be able to be played again and again, charm, and it needs to have that It Factor that eats at me, that makes me want to think about it, to write about it, to play it again and again and squeeze every bit of life out of it as possible, and after all that it needs to satisfy me, yet not satisfy me, to make me want to crawl through it one last time in the hopes of finding something, anything. A game I never want to stop playing.
Super Mario Bros. satisfies every condition, except for that last one. That is what separates Majora's Mask from the rest.
It has a better story, more varied gameplay, and is just as fresh and has aged as well as Mario. Maybe it didn't save the gaming world from extinction but a game shouldn't get a free pass just because it's a grandfather of gaming. Sometimes, there come new games that are just more interesting than Super Mario Bros. Majora's Mask has a lot of the same merits as Super Mario Bros. in its graphics aging well, its fun factor, its music, but it also invokes emotion that Super Mario Bros. does not, and it captures the heart and mind of the player that Mario, in all its platforming goodness, doesn't.
To top it all off, Majora's Mask refines the engine from its predecessor Ocarina of Time and tightens it to create a perfectly balances gaming experience, so it's technically sound as well.
I've said it before, and I'll say it a hundred times - Innovation cannot defeat perfection. And Majora's Mask is for my money as perfect a gaming experience as can exist.