Pretty good. I do have to say that it takes a while to get used to the controls, especially when you are playing both sides. Gamepad controls are much better than keyboard here. You could either add AI or make it that you can play online multiplayer. AI is probably going to be much easier, you really just need to make it so it moves into the direction of the ball when it's a certain distance away for it to work well with how simple the game is. You could use a raycast or something like that.
I enjoyed it.