Majora's Mask. To me, an adventure game is about atmosphere. This is why Okami is my favorite game of all time (well, maybe it isn't, I just say it is): It creates this beautiful world, with flowers and animals and so much to do. Ocarina of Time does a really great job of creating a really detailed and vibrant world, but it just falls short. While Okami had a kind of serene, peaceful, natural feeling, Majora's Mask had a looming, dreadful, haunting feeling (this was accomplished through the 3 day system, the settings, and the overall plot). Combine that with great dungeons and a variety of mask, and MM is my favorite Zelda game.