The warm-up mode is good for practicing ground strokes, but I feel a few additions would improve it.
Suggested additions:
Service only - lets you practice just serving
Return only
Opponent strike type - set which strikes the CPU opponent will hit, maybe tickboxes to select one or multiple (i.e if practicing smashes, set lobs only. if practicing volleys turn off lobs).
Machine instead of player - when practicing volleys, if the opponent doesn't return it, you have to wait for them to run back and then start the rally again. Having a machine that would send the ball over in quick succession in a random (or predetermined) direction would be useful.
Also an option to have a warm up before the match would be nice, with a button to "ready up". This could act as a kind of "lag/desync test" before online games too.