I have played Top Spin 1, 3 and now 4. Top Spin 4 is such a big improvement over 3 for numerous reasons. Some of these are the changing of the career calendar which allow for much more variety to the season. The games are much harder to play and offer more of a challenge, (I can get a solid difficult game on Very Hard as now as it was too easy on 3). There are still alot of well known players but I find it annoying that Maria Sharapova isn't in the starting rosters of the game and has been replace by one of the Williams sisters.
The game has also got rid of holding down LT and RT for power and control shots and instead have to hold the button down for power an tap for control. The game more than ever focuses on the timing of your shots and returns. Trust me this can easily make a shot too easy to return or make it a game winner. Coaches are available to help improve your game and give you special abilities (like greater top spin or being a longer rally specialist) to name a few, this again is a really good innovation and put an end to the spending points in specific slots for leveling up. Now you gain XP from matches and when you have enough you put it Into Baseline Defense, Baseline Offence, or Serve and Volleying. These will give you a permanent boost to your attributes whereas coaches are not and you loose their bonuses once you change coach.
Now there is the option of doing doubles tournaments and matches which for me is a huge plus over 3, still not able to put more that 1 player created player out there but still a big improvement for me.
I myself liked the little heart rate meter at the top next to the player but that is gone and replaced by a bar to show stamina which stays on the throughout the game, very small so not to really get noticed.
As ever the graphics are stunning for a 2k game as the normally always are, the improvement from 3 is huge I'm already hugely taken with this game. Very good game !Despite RAFA NADAL being OP!