I posted some suggestions but :
-Option to select your grip , a western grip gives you more spin , a eastern gives you better slice and volleys, etc...
-make the raquet type give you different attributes , with stats showing so buying a raquet makes a tactical difference not just for looks .
-take out risk shots and just allow people to use strategy to win games not pressing more buttons a must have , if you can move your oponent around then you can win .
-make a player with a lot of power use up stamina faster , the more tired they are the more errors they make , make it so playing on the day is more tiring than night , trow in wind element ,and put physics that make the ball fly different depending on the heat of the day (this would encourage better wall type templates with little power and lots of durabilty).
-able to select raquet's string tension and type of strings , make it so raquets can pop in the middle of a point as a random occurance .
-(not my idea) add crowd effect were people would uuuh and aaah on nice points and start screaming on important ones or long rallies , or right before serving for the match , set ,etc ...
-Make balls wear out with use and trow in the element of using new balls in between sets like they do in real life , a newer ball bounces more and travels faster , a deader ball stays in the court more and bounces less .
-challenge system , make the computer randomly make line call errors .
-better support for doubles games , like playing doubles with a team mate somewere else .and two oponents somewere else too , with random or preset partner setup.'
thats it

"It's nice to be important , but it's more important to be nice" Roger Federer .
"All who gain power are afraid to lose it , even the Jedi" Emperador Palpatine .
Venom400 the Classic Tennis player.