If you hold the shift key, the circular dial stops at 45° intervals.
Additionally, the little dot is an indicator of direction. (Although, I would put the "Rotation" circle dot on the right, not at the top, to indicate zero degrees.) This works well with gravity, as it highlights the direction of gravity. How would a slider indicate that?
I think the value should be a modulo of 360°, because 1080º is basically the same as 0°, 360° and 720°. That would solve the problem of huge positive or negative numbers.
Something seems weird though. To make objects fall downward, the angle is 180º. This makes no sense to me, as isn't zero supposed to be on the right side of horizon line?