This is the original Mario Tennis for Game Boy Advance, a surprisingly deep sports game. It's absolutely worth playing for its tight mechanics and character roster, featuring Mario, Luigi, Princess Peach, Donkey Kong, Wario, Bowser, and more.
The gameplay requires fast reflexes and strategic shot selection. The unique surprise is a full RPG story mode where you train a rookie, play through tournaments, and unlock characters. It's a fantastic package that goes far beyond simple tennis.