You can play either tennis or turbo skiing, which is more or less jet ski racing. The button swings the racket when playing tennis and accelerates in the races, but the game does everything else for you. The timing and length of your presses is the important part. Yes, it's simple, though entertaining nonetheless. Each sport can be played in single player and two player modes. If you're doing single player, there are tournaments and regular matches. The game stresses the training aspect, which is where you'll spend all the coins you earn (or buy – Namco would prefer that).
If you've ever played Wii Sports, this is a similar idea. The graphics are simple and cartoony, but it fits with the gameplay. It's free to download, and the button thing is a neat hook. Probably a good one for kids and those hopelessly bad at video games.