I remember when I played Smash Bros for the first time when I was a little kid, maybe about 8 years-old. I had no idea who the hell the characters were, what Nintendo was, and what I was supposed to do (I used to pick Mewtwo, he was the only one I recognized from the cast). I remember the sheer fun I had playing with my cousins, and that's why the series stuck in my head. It was several years later when I finally bought my first Smash, and now it's practically the only game I play.
I guess the point of this post is that, while some of you undoubtedly bought Smash for the sake of your favorite characters, I (and surely many others) had no clue who the characters were and, through the years, I grew to like them all. This appreciation of the character led me to try their games out, and that's how Metroid and Kirby are among my fave series now.