By and large, I think the game models players' real capabilities pretty well in its stats. However, there are some stats that just seem quite a way "off" to me. One example is Djokovic's serve and volle stats.
Djokovic's serve has power 50, consistency 49 and precision 47. Djokovic's serve is way more powerful than Federer's (who has power 41) and almost as powerful as Sampras (who has power 51). I don't regard that as realistic at all. Djokovic has a good serve, but it isn't that much more powerful than Federer's, and certainly not in the same league as Sampras. I think Djokovic's serve should be more along the lines of someone like Agassi.
Djokovic's volleys are also way too good in my view. He has forehand volley 39, backhand volley 40, smash 51 and net presence 43. By comparison, Federer has forehand volley 39, backhand volley 41, smash 42 and net presence 41. Overall, Djokovic's volleys in the game are on the same level as Federer's, he has a slightly highter net presence, and his smash is way better. Again, I think this is quite unrealistic. Djokovic is a baseline player who does not often come to the net, and while he is a decent volleyer considering his playstyle, he is certainly nowhere near as good in that department as Federer. I think Djokovic's volley skills should be reduced to be closer to players like Murray or Roddick, maybe a bit better.
My suggestion:
Serve power 43, consistency 42, precision 42. Forehand volley 37, backhand volley 38, smash 43, net presence 39. These are still pretty good stats, but they are not as over-the-top as the current ones.