Played the game beating most levels, getting stuck in 02-06 and 03-04.
The UI and graphics are absurdly polished and look fantastic. Honestly this looks like a completed game, so I don't know very well what kind of feedback you are looking for. I will give you some observations.
This could be only me, but after turning the game off I learned I was playing the game wrong by looking at your twitter. The way I tried to play was by flinging as little as possible trying to reach the right spot in one throw. Like golf, calculating each play before moving to the next one. Instead the game is supossed to be played with a lot of very short and very fast flings, it even rewards going as quickly as possible by giving the player extra stars when beating records. I got more than one star only in one level and that was because it was a straight line to the finish.
Even by learning how to play and booting the game again, I found the boomerang difficult to control and the game too punishing. The labyrinth level with the moths was particularly brutal. My brother who gave the game a try had the same experience. We might just suck at this though.
About controls, a lot of times I was going in a straight line ahead, holding and dragging my mouse in one direction and ended up with my mouse on the borders of the screen, making dragging and releasing in that direction impossible. This happened quite a few times and made the controls feel unwieldly. Have you considered hiding and locking the mouse to the center of the screen when not throwing? Also I found it unconfortable to use the right click to slow down time.
I believe you people are very skilled and will be able to polish this game to a shine. Good luck!