I played on Beginner, and overall I thought the physics and sound effects felt really good.
The main thing I struggled with was aiming the cue. Rotating it with the mouse felt a little difficult to control precisely. I also tried using the keyboard, and I wonder if it might feel better if the normal rotation speed were faster, while holding Ctrl slowed it down for fine adjustments. Another possibility might be to automatically slow the rotation when the aiming line is close to or touching a ball.
I also found it difficult to judge the right amount of power. I got a little better at it after playing for a while, but I often hit the ball much harder than I expected. For Beginner mode, maybe you could display a suggested power level that would roughly reach the target ball. It could work as a reference rather than an automatic solution.
One other thing: even on Beginner, having to pot more than 10 balls made the first goal feel quite far away. What if the first Beginner challenge only required something like 3 balls to clear? I think getting an early clear could feel rewarding and make players more eager to move on to the next challenge.
Those were my impressions from Beginner mode. I enjoyed the basic feel of the physics a lot!