Sorry I haven't been able to get back with feedback earlier, but here it is. First of all, good job so far!
I've tested all 3 versions of this and the current controls are definitely way better than what it was first. I noticed with the first build I was getting annoyed quite quickly and couldn't play it more than a few rounds, but with the current one I find the game hard to put it down; I think I'm beginning to enjoy it

My current highscore is 166.
It's nice that you earn extra lives after each reaching combo 5, but maybe getting a extra life for every hit after that is a bit too much. Also, most of the time I can only get the combos to reach that at the very beginning. Because of this most of my games go like this: I start off with a combo between 7-10, maybe I pull it off twice, giving me around 10-20 lives pretty early on. So maybe you can come up with something that balances this.
I think that the curve should have rounded corners instead of sharp edges, something like this:

Do you think that's possible? btw how do you make the collision shape of the curve? I thought we could only do circle collisions from the outside.
Another thing with the curve is that when you turn it really fast, the collision shapes probably overlap and the ball gets teleported to the closest possible location. Maybe continuous collision detection can help?
I found since the beginning something was weird looking about the game overall, but it seems that's because the scaling mode is set to stretch to fit, the balls basically look like eggs. Great to hear that you're working with a graphics artist. Is it only for the in-game graphics or the whole UI? I won't comment on the UI yet, because mechanics and gameplay seem to be the focus now.
Also, I managed to do this haha, the 2 purple balls fell off the curve at the same time and are stuck now.
