Nintendo opened an official site for Mario Tennis today. Access the site for a look at play modes, basic gameplay, character clips, Mii support, and wireless play details.
Modes of play include Tournament, Free Competition and Special Game. Tournament spans eight cups and includes single and doubles. Free Competition lets you select opponent, court, set count and other areas.
Special games include a number of special types of play, most notably Super Mario Tennis, which you play with an interactive Super Mario Bros. between you and your opponent. View a video at the official site.
Other special games include Ring Shot, where you attempt to hit the ball through rings, and Galaxy Shot, where you attempt to avoid holes in the court.
The Mii section shows the coordination options for your custom Mii characters. You can give your Mii special rackets, clothes, wrist bands, shoes and more. The game has over 200 items, unlockable as you play matches.
Wireless play includes local and internet play. The game also supports Street Pass. You'll be able to exchange Miis via Street Pass.