I'm impressed—I think you've done the best out of anyone I've seen or heard! Level 9 is the final level for now, so you've almost beat it all.
I'd be willing to bet your experience with the eight ball seeming to be hit too hard is because of the heavy (solid-colored) variants of the balls that start spawning later in the game.
I tried to design the levels to introduce those ball variants in an intuitive way. For example, Level 5 (Flood) is the first place where they appear. I structured the level so that the level repeats itself, once with the lighter striped balls, and again with the heavier solid-color balls. I also designed the spawners so that the player would be virtually guaranteed to have either the eight ball or cue ball experience a collision with both variants.
I like the way heavy balls are introduced, but this is probably something that really needs text if I want players to be able to figure out, just because it's totally non-obvious that striped vs. solid would be anything other than a cosmetic difference (and you might not even notice the cosmetic difference). It's not like anyone is expecting to see "elite enemies" in a pool game...
I wanted to make sure losing the cue ball was a least a little bit punishing, but it would be really easy to dial the respawn threshold back, so I think I'll do that based on your thoughts.
I'm really glad you liked it, and thanks for the feedback!