HDR is like Marmite you either love it or hate it. Used properly it can work for many images.
If the image needs the 'Gothic' treatment, then you can go to town like this one.
http://www.flickr.com/photos/chris-judge/5579790149/in/photostream
But HDR can even out harsh Midday light as it even out the shadows like this one
http://www.flickr.com/photos/chris-judge/3708209316/in/photostream/
It means you can shoot at any time of day.
It works with mechanical things
http://www.flickr.com/photos/chris-judge/5880034781/in/photostream
It works to bring out all the detail even when there's no Dynamic Range reason to use it.
http://www.flickr.com/photos/chris-judge/5880034317/in/photostream
With this one it was used to enhance the feather detail and to open out the deep dark shadow cast on the Owl's right eye (as we look at it)
http://www.flickr.com/photos/chris-judge/5620474268/in/photostream
It can capture light beautifully, here the Dynamic Range is captured (B&W this time just for variety)
http://www.flickr.com/photos/chris-judge/5539626737/in/photostream
There are many reasons why HDR can be a really useful tool, but it's like driving a Ferrari you have to be very light on the controls or it will run away with you. I hate HDR with halos around everything.
With all Post Processing you have to have an idea in mind then work towards it and know when to stop, this is really important with HDR.
Chris