Fun little game. Like others, I found the mouse look to be a bit off putting. How you can improve it next time is, instead of setting the camera's rotation to the mouse position on screen, (which I'm assuming you are doing) add the input from the mouse to the current rotation. Something like:
targetXRotation = camera.transform.eulerAngles.x + Input.GetAxis("Mouse Y");
targetYRotation = camera.transform.eulerAngles.y + Input.GetAxis("Mouse X");
camera.transform.eulerAngles = new Vector3(targetXRotation, targetYRotation, 0);
This is off the top of my head and haven't tested it yet but it should point you to the right direction. Also one of the inputs will have to be subtracted instead of added due to it being inverted.
Good Luck on future updates!