I've seen some pretty dramatic skies in the Dakotas and in Louisiana. I saw a wall cloud similar to this shot in North Dakota but not nearly as symmetrical. Either way, you look at it it is a great photo. As for HDR, it's as valid a photo technique as exposure bracketing. Many cameras are including this setting and some do it without you even realizing it as part of the normal photo taking process. Nikons compare every shot you take against a database of thousands of lighting situations and choose the best exposure based on saved and real time data. This is all done instantly by very powerful processors built into the camera. Progress!