I saw it in the shop and I was looking for a fun new game for my 3DS (finished and played 250 hours on Pokemon X). I remember a friend of mine saying about 6 years ago that she loved the game. I thought it was worth a shot. It was one of the best (and worst, because it is how I procrastinate) decisions in my life so far.
I voted "other." I started with WW back in 2007. I had a Nintendo DS Lite and, of course, I would browse the game selection when I was in a store that sold video games. The cover looked cute and that's what drew me in. There aren't many types of games I enjoy playing, but I figured Animal Crossing was right up my alley. Normally I stick to the classic Mario Bros games and word/puzzle games. No regrets here!
A friend told me about it and we got totally crazy for the date the game would lie in the stores. After that I found out about LinandKo and their letsplays and I even got more excited.
I don't remember how I first heard of the game, or if my parents just bought it for me. I have a feeling I bought it in America (I'm from the UK) when I'd just gotten my DS Lite for Christmas before our holiday there. This was Wild World, back in 2005/2006 when I was around 12/13.
My parents surprised me and my sister with a GameCube around the time it came out and they had bought us some games for it. Animal Crossing happened to be included and I've owned every NA version since.