Thanks for playing!
The boomerang constantly rotates around at a constant speed; this is intentional as it helps you line up throws around obstacles, and keeps you on your toes indeed. If you stand still, you can see what the radius of the rotation is, but we might add an option to display it.
About the rocks, one tip is that obstacles always have shadows - big ones. These should always be visible as long as you have the quality settings set to Medium or higher (the game isn't that performance-heavy I believe, so we recommend just setting it to Ultra).