I've been playing this game now for a while and I can think of atleast 2 things that may need a look into.
First thing is the serve. As things are now, bombing down serves is too easy. A lot of players feel this and so even if they for once happen to miss a first serve they continue to bomb down a second serve ace at 200+/kmh. I realise this can happen during a real tennis match aswell in matches with great servers, but certainly not to this extent. In the real world, tennis players are careful when they serve a second serve because they can't afford to lose a point on reckless play. In this game it's not reckless, it's just another high percentage shot that gives the server a too big advantage if the returner happen to get a racket on the ball to start the rally.
Now a bit of complaining on the returners end. I think the fact that people can press down their strike button when recieving to automatically move in the correct direction kills a bit of the skill needed to execute a good return. In the real world, being good at returning serves is a major weapon in a players arsenal, an example being djokovic. Players would be careful when serving to him because they know how consistently good he is at returning serves. It should be a skill so that when someone plays player X they know to be careful when serving to him. But in this game, anyone can return like djokovic if they get fed up having to rely on their own reflexes.
These 2 points contradict each other a bit i know. But these are the things i've encountered when playing and it's not things that i do because i'm enjoying a bit of realism aswell, and so i don't mindlessly smash down huge serves on second service and i don't keep my strike button pushed down to give myself superhuman reflexes when returning. I don't enjoy it but maybe other players do.
Maybe it's fixable or maybe it's not, but i thought i'd atleast raise the point.
I like to end this post on a positive note so i thank you for making this otherwise really fun game for people who enjoy tennis!