Did you connect your mouse with bluetooth or with the Unify dongle? In my house with bluetooth it doesn't work well. With the Unify dongle no problem.

The mouse wheel has two modes: "step-by-step" or "free rotation". Step-by-step is what you are used to from most mice (locks in place in small steps), with free rotation the wheel continues to run even when your finger is no longer on it.
Simply press the mouse wheel to switch between the modes.

I have the mouse and no problems with it.
Do you have the mouse in free run? It is very sensitive. Sometimes the picture scrolls slightly when I move the mouse. But then I have to move the mouse roughly on purpose.