Mirroring games from your iPhone to your Apple TV with AirPlay is great, but it's still just what's on the small screen blown up on the TV. This isn't the case in Motion Tennis. With this game, the mirrored content is something different to what's being displayed on your iPhone, which opens up a whole new experience. Think Nintendo Wii style gameplay, only using your iPhone as the remote, and your Apple TV as the console.
The first thing you need to do is to enable AirPlay mirroring on your iPhone; double-tap the home button and scroll all the way over to the left. With this on, when you go into the Motion Tennis app, you're presented with two different views. The menus are on your iPhone, with your player standing, patiently, waiting to play on the TV.
That's key to the whole experience. Navigating menus and selecting your games is done on the phone, there's no icky on-TV navigation. As soon as it's time to actually play, the phone display turns into a pause button and it's time for Tennis.
Gameplay is all motion based, as with the Nintendo Wii. Simple motions across from right to left, left to right, or with a slight arc complete the different shot types, and where the ball goes is largely based on your timing. But it's easy enough to get the hang of. Get the initial learning curve out of the way and it's a true pick up and play experience. AirPlay mirroring is smooth, and relatively lag free, and your swings are pretty much reflected in real time on the TV in front of you.
I love Motion Tennis. It's a great idea, well executed, and hopefully sets a precedent and gets more game developers looking at innovative ways to put the Apple TV to use. For now, enjoy it. It isn't the cheapest game out there, but it's fun to play and is definitely something different. Just be sure to hold on to your iPhone tight!