Easy to cheat, and bad physics
Outside of there being no sound and poor physics, it's really easy to just 'push' the puck over the computer side and into the goal, so no challenge there. One: your circle should be limited to your side of the board. Two, and most important: there should be some decent physics, so that when you hit the puck from the side with your circle, it doesn't just go straight back. Knocking the puck toward the sides of the board is the 3/4 of the strategy of air hockey. And three: there should be a goal slot, not just the whole other end of the board.
This isn't air hockey, it's soundless Pong with worse controllers. Get it together, man. Surely you can do better than this.