The best multiplayer game ever.
I've been playing this game since it came out in 2001, and I am yet to get bored with it. Because of the huge number of people who play it, the gameplay is always changing and evolving. Given the wide array of characters, items, attacks, and stages, someone will always try something you've never seen or thought of before. I've never understood why it was rated Teen; the main focus is on fighting, but the actual fighting is bloodless and involves knocking your opponent off the stage, rather than damaging him until he dies. If you can hold the controller without taking a break to suck your thumb, then you're old enough to play.