Arguably the darkest and most mature Zelda of all, a wistful and twisted rumination on friendship, depression and the myriad of human reactions when faced with impending, inevitable death. A game in which "saving the world" means actually saving the people that inhabit it, and helping them reconnect with one another - that's the true strength of the game, showing how important the connections we have with others are, and how those connections make us human.
Often overshadowed by the mythical, genre-defining Ocarina of Time, Majora's Mask is a completely different beast wearing a very similar skin - far from the "epic quest" template its older sibling mostly has, MM opts for a far more intimate, often off-kilter and psychedelic, tone. And the game doesn't chicken out of hitting you 'right in the feels' - one of the most poignant themes of the game ends up being that, no matter how hard you try, you just cannot save everyone. You just try to make the most good you can.

Even though its temples aren't among the greatest of the series (though you might personally disagree) and the 3-day-time-limit is everpresent (though manageable through use of the Song of Inverted Time once you get back your ocarina), gameplay feels like a refined version of OoT - young Link has more items in his arsenal and masks this time are an essential component of the gameplay, from the 'main' ones that transform you into a Deku/Goron/Zora, to other ones who still give some powerup or special power, to some that are purely cosmetic but are relevant to advancing certain sidequests.

Speaking of sidequests - they might be the best in the entire saga. The development of NPCs in this game hadn't been seen in a Zelda game before and some of them have emotional arcs that resonate even today. Shouts out to Anju & Kafei, Romani & Cremia, and the little girl with his father in Ikana Valley, some of the finest and most emotional arcs I've experienced.

All in all, a flawed masterpiece in my eyes, with some of the most mature themes you can find in a Nintendo game.