I love the game now, but I remember finding the first few hours really, really frustrating. I wonder whether it would be worth putting some work into the presentation, because the tennis part of the game is so much stronger than the menus and documentation.
A few things like:
1 * ALT by default seems to move in the menus - so that doesn't let users Alt-TAB.
2 * Gamepad support works, but I feel a lot of new players (perhaps most) would be using a game controller rather than a keyboard. All the docs seem to assume keyboard.
3 * The menus are generally very clunky. Navigation in the menus is strange, especially with a gamepad. I resort to the mouse, it's easier.
4 * All this talk of b1+b2, b1 - etc is quite confusing. I'd just label them slice/lob/risk shot, etc. Nobody reads the docs sadly
I mean no offence, and I don't want to sound negative. As a fan, perhaps some of the simple things could be improved and it'd help make a much better first impression. The game should be so much bigger than it is!