Everything that Kaiaa said is so much fun! I enjoy planting trees and flowers in specific places to make my town look as nice as possible. It's also fun to collect all of the fruit. I love running errands for my neighbors as well as simply walking around and listening to the music. I love the Game Cube version's music, especially the rainy day music. I could listen to it for hours. Finding visitors like Katrina is also fun. Basically, there is a nearly never ending amount of fun things to do!
Also, it's not called "Population Growing." It's simply Animal Crossing.