Progression is rough. Having to rebuy all the upgrades at every stage isn't great. Especially at the stone stage where 4-2 doesn't get you a new upgrade and you have to reach 4-3 to get to the fifth stage, only to do it all over again with just a wheel spin to show for it. Went back to first stage to get the third star and it gave me an achievement. It gave me the 1.2x achievement multiplier but I expected a bit more from it. The wheel spins also feel a bit unfair, I don't know how much faster my progress would be if I had better wheel spins. Feels like getting punished by the randomness. Even if you had the theoretical best spins you wouldn't know it.
Look and feel of the UI is perfect, and the sound design is amazing too. Love the unique sfx on every stage.
Sorry if this is harsh, just sharing my experience. Overall it's still fun but at 4-2 I tapped out. As I understand from your dev log linked below there will be global upgrades in an upcoming version so most of my concerns are probably addressed at that point.