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The gameplay is pretty straightforward, but takes A LONG time getting used to.
To hit a ball, simply swipe your finger in whichever direction you want the ball to go. It sounds simple in theory, but is a little testy in practice.
I'll admit I was so frustrated with the game's responsiveness the first few games that I strongly considered deleting the app, never to play it again.
I decided to stick with it because well, I love tennis, and there aren't that many (are there any really?) tennis games on the iPhone.