"NH" is a self applied label, which accounts for the wide vareity of techniques and practices included under the umbrella.
In a very generalized sense, "NH" eschews harsh methods and coercion and instead emphasizes communication and partnership with the horse, by trying to understand how horses interact inside a herd.
Not new, not radical, just ideas that has been around since Xenophon, but everything old is new again.
Like most training methodogies, there is something to learn from most NH practitioners and techniques, even if you don't want to endorse them wholesale. I've read/watched Monty Roberts, John Lyons and Buck Brannaman and learned something from all of them. Doesn't mean I'm going to do an appreniceship with them, style myself after them or endorse their whole programs, but there is some solid stuff there, and likely with a host of others I haven't read.
Since the 90s, a lot of self-styled NH trainers have very agresseively marketed their products to novices and backyard owners in a not terribly straightforward way, which has given all of things associated with NH them a bit of a black eye and shady reputation.
Also, new converts to NH tend to have a overzealous approach and want to go out into the world as evangelists and tell other horseman that they're doing it wrong. This does not endear NH to other serious horsepeople.
If I wanted to sell a book or DVD on training at this point, even if all it contained were NH ideas and techniques, I'd call it something else, just to avoid the stigma. Maybe Transcendental Horsemanship? Maura's Five Fold Path for Equestrians? Celestial Horse Handling? Anythign but NH!
As always, just my opinion, just my .02.