Both Black Christmases have been underrated on release - the original wasn't really picked up (except in Canada) on release in 1974 and has become a worldwide sleeper "hit" in the years after its release, mostly by word of mouth - mainly aided by being so copied in other films such as "When A Stranger Calls", "He Knows You're Alone", "Halloween" (all films I love) and many others since.
The new version is obviously based on the original so those who deride it for being "just" a 'bunch of girls in a house with serial killer' should know that the original Black Christmas invented this sub-genre of horror and the new version was obviously going to be the essentially the same setting otherwise it just wouldn't be "Black Christmas". (The original was also the first film to introduce the now common "twist" and the new version rightly doesn't make too much of this as its also been copied so many times since).
The new film has some differences (as well as death scenes) - after all, there's not much point in a shot-by-shot remake (the awful, pointless shot-by-shot remake of "Psycho" comes to mind). Just as the original broke new ground in camera work (copied to worldwide acclaim in "Halloween") the new version uses camera angles that make you take notice and disturb your senses. The twinkling Christmas lights (and lighting) are also used to great effect to grate at the viewer's senses and introduce a sense of unease in the viewer that is ultimately more disturbing than just gory deaths (which there's plenty of). Just like the original, the Christmas music becomes a haunting backdrop.
Just like the original, and after all real life, not all the characters are 'likeable' - which allows for different reactions to deaths and questions afterwards. Also, you don't necessarily have the predictable 'last girl alive will be the non-drinking, non-smoking, non-swearing virgin' scenario.
Bob Clark, the original director of the first version, not only visited the set but also gave his personal thumbs up on the new take of the story, both before and after the film was made. It took many years before the original version was given the recognition it deserved, most describe it as a classic and rightly so. Maybe in time the right audience will find the new version of the film and appreciate what it was doing, it's not as perfect as the original, but its not too far off it.
Both versions are definitely worth watching more than once and certainly worth the cheap prices they're now both available at. If you haven't watched the first one (and you should), you can still enjoy the new 2006 version - just take on board that yes, it's a group of girls in a house about to be picked off one-by-one, but its about to be done with style that all too often is lacking in hack and slash films...