There are a number of different sub-styles of dark ambient, some of which are clearly variations on heavy metal or industrial music, while others sound like the evil twin of New Age ambient. Dark ambient is intended to be beautiful- in the sense of Baudelaire's “Flowers of Evil”- but it is not intended to be pleasant. Many people like to use New Age music to for meditation or deep relaxation self-hypnosis exercises, but if you tried to meditate to dark ambient it would be more like performing a black magic ritual!
It's certainly not for everyone, and most New Age fans probably wouldn't take to it. However, if you're one of those people (as am I) who can find the beauty in ugliness and the art in discordance, then you might want to consider giving dark ambient a try. Open up a volume of H.P. Lovecraft while you listen, if you really want to freak yourself out a little!