Some key areas for improvement for me:
1) forced errorsAt the moment, it seems it's either a winner or an unforced error. In real life I think, players are more often than not forced into making errors. For example, an inside out forehand cross court stretching opponent far off the court, forcing them to net the ball.
2) better sense of fatigue as the match progresses This is where different styles would really matter in terms of game play, as a Nadal style would be able to force opponents into errors through great defense and countering, outlasting them with consistency and fitness, and a Federer style would be trying to end the point as quickly as possible, wrong footing opponents with crazy angles. I think stats should degrade over the course of a match, how much they degrade being down to their fitness, the length of the rallies, and the length of the match.
3) change hit winner system At the moment, I can easily, with little risk, pull off crazy angles, but opponents tend to get them back more than they would in real life. Winners should be harder to pull off as they should be risky, but when pulled off, the chance of being a winner should be a higher. For example, Nadal, in his prime, had a monster forehand, but often played it safely, either forcing an opponent into errors or waiting for them to make an error, meaning less winners but also few errors. Federer, on the other hand, prefers to go for it more, risk more, meaning more winners but also more errors.
4) body serveThe body serve is a great weapon in real tennis, particularly on key points in a match. It doesn't seem to work though in this game.
5) wrong footing an opponentI think more stats for movement would be great. From point A to B, Nadal seems to run faster than Djokovic, but Djokovic can change direction more quickly. It's easier to wrong foot a player like Raonic than Djokovic, and I think there should be a stat for it in the game.
6) slice needs to have it's own statsThe slice is a very important weapon in tennis. Different styles use the slice differently though. Nadal uses his slice to slow the point to get back into a rally, employing a fair amount of backspin, making it hard for his opponent to smash winners. Federer, on the other hand, uses his slice more aggressively. It should play more of a role in the next game I think.
7) nervesNerves play a huge roles in tennis. What about making it into a stat? For example, the nerves stat could enhance or even hurt a player's ability to play at key points, such as at 15-40 at 4-5 in a set. A great example would be Nadal, who (in his prime) would often win the same amount of points as his opponent but would win a higher percentage of the important ones. Players like Nadal play better under pressure (at least he used to). A stat that reflects this would be great.
8) more stats for forehand, etc. For example, backhand cross court stat and backhand down the line stat separate. Djokovic's backhand down the line, for example, is noticeably better than his backhand cross court, and Nadal's backhand cross court is excellent but he seems to struggle to hit it down the line with the same kind of accuracy. Such stats would make matches play out more realistically I think.
9) spin should affect game play moreStats for topspin and backspin separate, and should also be separate for each wing (forehand and backhand). More backspin means it is harder for players with less spin to effectively strike the ball. More topspin equals more consistency and also puts ball out of strike zone, forcing players to risk more by moving closer to the baseline or play the ball far behind the baseline. Less topspin results in more errors but puts opponent under more pressure, as the ball is travelling faster and moves through the court more, but also makes it easier to counter. I think this would further play into the different court surfaces as well, making some styles more noticeably better on certain surfaces.
10) court depth of shotsThis stat would affect how easy it is for a player to get the ball deep in the court. A player like Djokovic would be high in this stat, but a player like Nadal wouldn't be. This stat I think should be given to forehand and backhand separately.
11) more shot optionsI think you should be able to add power to any of the shots (topspin, flat, slice), giving greater variety to the game play. Using power button with slice, for example, could make it an aggressive slice. Adding power option to both flat and topspin shots would make points play out more realistically I think. For example, Nadal usually plays it safe (normal topspin), but will use power topspin when he wants to get into a good position and sometimes finishes with a flatter power shot.
12) more shot animation options/statsFor example, the stroke a player uses on the run doesn't look the same as one they play when they already in position. This could be a separate stat as well, as in some players can play better shots than others when not in position. Del Potro's forehand is better, for example, than any on earth when he's in position, but Nadal has a better running forehand.
13) AI personality options for playersThink games like Fight Night Champion. It would be great to have sliders that alter how a player plays when not controlled by a human. Players tend to have specific strategies, and it would be great to have this reflected in the next game. For example, Nadal hits his forehand almost always cross court to his opponents backhand and only goes down the line later in the rally or when the court opens up. Sliders could also determine things like how a player behaves when down in a set or when they are ahead.
14) serve should matter moreThe serve matters in the game, which is more than I can say for pretty much any other tennis game I've played. However, I don't feel I have the advantage I should have when serving in the game. Serve return should be a seporate stat. Player's like Djokovic are a servers nightmare, but for the most part, big serves equal poor or no returns. There should be a serve spin stat I think too, the spin affecting how easy it is to return the ball, much like the speed.
15) movement animations These are all the key ones I can think of right now that would majorly improve the game. I think these are more important than graphics and adding non game play elements. Of course, if none of these see daylight in the new game, I'll still buy it
. It's an awesome game as it is, so any improvements would make it a must by!