Quality, consistency, and timelessness.
OoT, by all counts, is a well-designed game. Length, audio, visual design and variety, gameplay, everything is, with few exceptions, is pretty far North of "simply functioning." The bosses are fun, (and at the time, finding bosses that both behaved uniquely form general baddies AND actually functioned without odd and awkward tactics like literally tapping their asses until you strip them of their flesh [http://www.youtube.com/watch?v=JxrsxN42fVk] and the game in general makes good use of most of the new toys it gives you. There's a lot of variety in gameplay without making it a level-based action mish-mash like many of its contemporaries. (in under a minute and without teleportation, you could go from fighting a shadow version of yourself in a mysterious abyss to a surprisingly fun fishing sim)
Generally, the worst things you hear about with the game are Navi, the Water temple being over complicated, and having to go to the menu to switch apparel. (AKA: the Water Temple Strikes Back, part: Boot)
Are they really that bad? Nope.
And of course, consistency is consistency. Great dungeons, fun characters all around, nifty weapons, the storyline becomes more complicated in a logical manner, and of course, it manages to feel like the same world, all the time. I can envision the annoying Mido from the Kokiri Forest existing simultaneously with Daurnia, Kaporea Gaborea, the princess, Ganondorf, or even the dungeon bosses like Volgiva, because they feel like that's the kind of menace that would be in the fantasy world they live in.
The only time the player is plunged into a drastically different mood and environment really is the Shadow Temple, but years later, I'm still not entirely sure how to feel about that one.
For both the first and third points I have to make,interacting with the world is quite intuitive, and even though you can definitely tell from which period in gaming history it came from, a kid just now coming of age to start gaming could easily slip into it and have fun without the jarring, generation-before-you-started-gaming experience I'll admit I had when I first played ALTTP.