A good start

Not shabby for a free/advertising game at all. A little more depth to the tennis strategy would be great, for instance a lob shot to force the opponent back off the net, certain opponents that have weaker backhands, forehands, left handed shots, or even that are worse at down the line serves, so you have to experiment each match. Add those features and Id certainly be willing to pay to remove the adverts and add other features. Also it might be good if the direction of your swiping mattered a little bit more, easier to hit out of bounds, but then add in random unforced errors and double faults for the opponent to balance it out.

M the immune about Stick Tennis