We've all seen this phase: Like Nothing You've Ever Heard. Whenever I read it, I always think "this artist doesn't listen to enough music". That isn't a bad thing until you want to explain to others what you sound like.
Music is highly subjective, and often difficult to explain. But it is quite rare when music comes along that is truly unlike anything we might have heard.
It is said that when Igor Stravinsky first attempted a performance of Le sacre du printemps (or "The Rite of Spring") about a hundred years ago, some of the crowd booed, others argued, fistfights broke out in the aisles, and much of the music was unheard after a point because of the rioting. Eventually the police were brought in to subdue the crowd.
The fact the there is still quite a bit of debate over what exactly happened (and why) at the show that night, leads me to believe that the audience truly experienced something new; they were not at all prepared for it, many of them apparently had no reference for it, and it led to some surprisingly base emotional responses. It also means that you can't blame that sort of thing on rock ;)
Over time, some have said that none of the rioting at Stravinsky's performance ever happened. I think this is also a response to something so new we cannot immediately accept it; so we dismiss it altogether: it never happened. This is akin to those who believe we never walked on the moon. It seems impossible, so it could not have happened. And because we have not been back, in some ways it remains a new idea.
From these examples I glean that perhaps an artist doesn't want to state such a thing - "Like Nothing You've Ever Heard" - unless they want to be unpopular or at least controversial for a decade or so! In any case, as artists and musicians 'new' doesn't happen as often as we'd like in our own creativity, and perhaps we are better off leaving explanations of music style to more objective ears, if we can find them.
A different example of new: What Björk is doing with her new release Biophilia is new, but perhaps not so much musically groundbreaking as technologically (the first App album, I believe). We'll have to wait and hear it all to find out.
Not even what Bach did stylistically was new - he was just a better composer than most writing in his day, and a gifted improvisationalist.
My group Gravity Tree strives to be original, and we're on somewhat of a mission to explore what's new - new to us as musicians, as songwriters. However, we're the first to acknowledge the scores of influences. We hope we've never been misquoted with a "Nothing You've Ever Heard" phrase, and we'd never say it.
I might struggle with what to call the music I make. But I cannot worry too much if anyone has heard that kind of thing before, or if someone thinks it sounds 'old'. Old is as subjective as music itself. Is '90's music old? Are the Beatles old? What about Mozart? More importantly, does it matter?
It may not be "Like Nothing You've Ever Heard", but as long as it is not "Exactly Like Something You Just Heard", I believe I am on the right path.
The best thing to do is to put out the music you enjoy making, and hope others enjoy it also. And listen.