It's not a very deep mode. On ps3 square is backspin and circle is topspin but I honestly can't tell the difference between the two when I use them in this game. They don't appear to move any differently, it's just the way your character hits it that appears a bit different. It's pretty janky too, there's a lot of times where you'll swing and your character will wait until it's past him/her to swing (and miss obviously).
It's still fun for what it is though, it's not like this is a dedicated tennis game. I played my friend last night and we had some fun. I even managed to hit a drop shot right over his head when he was crowding the net which made him rage pretty hard :lol