Shutter priority practice

I have been practicing taking shots using shutter priority mode to get the blurry effect of moving objects. I took this photo (this was the last out of about 50 different shots) with a 15 second exposure and thought it came out fairly well, then I did a little cropping and voila!

The original shot in its unedited form is:

I needed a dark background for the running water to contrast against, there was a facecloth nearby so I used that. The settings used were:
Nikon D7000
Shutter priority
Shutter speed 15s
Aperture f36
ISO 100
Metering Matrix
Focal length 75mm
Focus mode Manual
AF Area mode Single
Tripod
Shutter actuation Remote

Let me know what you think, or if you have any ideas or tips on how I can improve, thanks.
Marc