It's why MM is so incredible.
You also have about 40 NPC's around the game world. EVERY SINGLE ONE has a sidequest to complete. And these aren't just simple ones. For example there's a famous quest involving two lovers, anju and kafei. Kafei's body has been turned into a child's body by Majora, and so he has run into hiding, ashamed of himself. You have to find him, try and fix his curse (and fail), and eventually bring them two together to get married. You finally acheive this, but it's 20 minutes before the end of the world.
You get a mask for your trouble, but they both end up doomed regardless. And you can't stay - you have to go back to Day 1. And guess what? Anju and Kafei are reset. If you don't help them this time (which you wont), they'll die apart.