My first attempts at ND filter shooting; this is with a Polaroid variable filter. It's not the best quality, but seems to be decent except for some unevenness in the density when I set it at its extreme max. I didn't want to spend a lot of money until I tried it to see if I was going to use this style of shot often enough to be worth the investment.
Constructive comments welcome!
I would say that the harshest hit to the quality and clarity of the photos may be the filter that you are using, they look flat.
On a side note, as far as shooting with the ND filter, try expanding out from the creek or river as you shot in these images. Try a body of water such as a lake or an ocean, and don't be afraid to look up too, on a windy and cloudy day a long exposure can make the clouds appear to be like watercolor paintings, in the right landscape and composition this can be very positive for the effect.
All in all I would suggest browsing around images on this thread to see what you find inspiring, and take some ideas that others have shared and try them with your own photography.