I agree with Dave@ and JooB. Your concept is great and you began well -- keep at it, if you can, with the same model and similar/same conditions by adding different maneuvers to get some variety. Do NOT pay attention to any detractors that question your vision (bad setting/environment, bad props, bad concept, etc.) unless they can contribute to the problem, as they see it. In my opinion, criticism that is not constructive is not very useful.
As you learn more about video and photography, you will find that all the manual controls and add-on accessories are simply tools for you to get the results you have in your mind's eye. To that end, ND filters are simply a tool to get the exposure you need for the image you want. Generally speaking, ND filters are used to darken your exposure for many reasons: you have bottomed out on your ISO, your shutter speed is to high, your aperture is too small (large in number) giving you too much depth of field. This last one is the primary reason most cinematographers use them, to gain a large aperture, throwing the background/foreground out of focus. Which presents a new problem -- keeping the subject in focus as the camera moves closer/further away. (BTW, do not be too cautious of higher ISO. Today's sensors can easily give quality images at low and midrange settings, and when all you have for low-light situation are high ISO settings, you must choose to shoot less than perfect images, or none at all.)
It is always helpful to learn technique from courses, but try to take courses that explain Fully, the technique, so that you learn the WHY as well as the HOW.
Keep up the experimentation -- you are on the right path.