... cool shots, but some of them are almost OVERDONE imo. First one is awesome though!
Most cameras only do 3000:1 contrast ratio from darkest/brightest... HDR uses 3 or more exposures to create detail in the brightest and darkest areas. replicating the full dynamic range of colors your eye sees (think of when you look at a building where the sun is just over the roof... if you look too long at the sun, you cant see in the shade, and vice versa)
The more "natural" it looks to your eye, the nicer... I think
Here's one i took in Germany
This next one's in Switzerland ... notice the colors on the apartment on the left.. which normally would be black with normal single exposure: