Majora's Mask is great for its gameplay, its characters, the atmosphere, and the story. Even though seemingly 95% of character models from Ocarina of Time are borrowed for Majora's Mask, this time you are far more invested in these characters. The sidequests are numerous, each one letting you learn a little something more about the personal lives of Termina's inhabitants. You become familiar with what everyone's dreams, aspirations, and troubles are, and how they try to meet or solve them in what little time they have left, whether they may know they're doomed or not.
The story lends to the atmosphere as much as the setting (Termina) itself. It gives me a tribal vibe with all of the ceremonial masks, and their importance. The world is going to end, and you know exactly when it will, to the minute and even the second. The world and the music is often eery and foreboding; you are always reminded that the clock is counting down. There's always an underlying sense of urgency, even as you are free to begin again from Day 1, withy 72 Hours Remaining.
Personally, I like to take my time with this game. I've never beaten it really fast; it can take a month or two for me, usually, if I'm really set on beating it. I'll always stray aside and fill out my Bomber's Notebook. One thing I've almost never bothered to do, though, are the Great Fairy Collection Quests for the temples, though the rewards are great.
I think that Majora's Mask will endure as a great game. It took the same engine, character models, and overall visuals from Ocarina of Time and still gave us a vastly different, unique experience. I'm leaving this as a short review. It's a small tribute from me to my favorite game in the Zelda series. I'm looking to Skyward Sword, and the future of the Zelda series, with a hope that I can love what's to come as much as I did Majora's Mask.