So I've been playing TE4 on and off for about a year and a half now, when it still had TEM2's graphics and TE2013's menu (how times have changed

) and I'd like to make a few suggestions.
1) The Topspin skill is still not where I'd like it to be. Unless you are playing as a Defender style, heavy topspin shots are quite easy for the opponent to attack with shoulder height accelerations on the forehand, some of which can reach 110 mph/177 km! Balls that are short and high bouncing are essentially free points for the player attacking them. Due to the way that shoulder height accelerations are implemented, I beat players with a high topspin character by just attacking their backhand all the time and never going to their forehand, which is just far too dangerous, even if their backhand has better stats.
2) The normal strike and topspin strike are not very effective currently. I've always believed that the normal strike or topspin strike (if using high topspin skill) should be the most common strike during rallies and the acceleration a riskier shot that can finish a point or put the opponent under serious pressure. Currently though, accelerations are not much less consistent and precise than normal strikes and hit a lot harder, making them the obvious choice for the majority of shots. Since normal strikes are quite slow, they are usually easy to pick off with accelerations. Topspin strikes have the same problems as normal strikes, but with the added problem of shoulder height accelerations that I mentioned in point 1. I don't believe that accelerations should be "nerfed", as rallies are long enough as it is and defensive players would become too strong, but the normal and topspin strikes should be more useful.
3) Players who play far behind the baseline should face penalties on their shot depth and speed. I've noticed the AI standing way behind the baseline and still regularly hitting deep hard shots. I can also do this to an extent too.
4) When serve/volleying, I still see my character often hitting groundstrokes when trying to volley a low shot, rather than a low or half volley. This almost always leads to an error. I'm pretty sure this is a bug, especially since you've added those nice half/low-volley animations.
Otherwise, great job Manu. It's impressive to see what a dedicated person can do on a budget. Even in its alpha state TE4 is far better than any big budget tennis game released in the last decade. Keep up the good work! I'm looking forward to the programmable AI and tournament mode when that arrives.