General gameplay:
Top spin bounces a bit higher, Slice curves the most and bounces low, Straight is the fastest but most predictable shot.
All shots can be charged for more power. Hitting the shot button twice gives you a bit stronger version without charging it, isn't as powerful as a fully charged shot, though.
A fully charged shot knocks your opponent back by a lot unless he answers with a special shot or with the appropriate shot. Return Slice with Top Spin and the other way around and Straight with Straight to have much less knockback.
You also have a Lob and a Stop Shot. One goes high and far back, the other stops shortly after the net. Especially a charged Stop Shot dies very quickly.
If a ball is returned badly or very predictable, a star icon will appear on the ground. Return a ball from that position for a very powerful shot.
Charging shots gives you meter. You can use it to either perform those sniper shots from a star icon position or to slow down time to get hard to reach returns. You can also build meter with Trick Shots, which are mostly some kind of jump to a position, depending on what direction you flick the right stick. Time them badly and you'll lose meter instead. It's a risky swag tactic go gain meter quickly.
Finally, if you have full meter, you can perform a Super Shot. Those are super hard and fast and can also be aimed. It's basically a guaranteed point but costs the full meter.
The aimed and Super Shot can get returned but require really strict timing. A badly timed return will either damage the racket of the opponent by a third or break it entirely in the case of a Super. You only have a limited number of rackets and if none are left you are K.O.'d, instantly losing the entire match.
Another thing is meter management. It can be better to let the opponent score than wasting your own meter to reach it or damaging your racket.
The characters all play differently, courts play differently and some have gimmicks and it's an entirely skill-based game that required some strategy. Overall, pretty good.
The only thing I don't like so much is the music. Especially in Adventure Mode it gets real old real fast to have the same music loop on the map screen.