I don't realy see what kind of new format could be added anyways. The 20th century had some kind of detonation of styles, suddenly a lot of new stuff came up, and I'ld say this happened for two reasons:
-New media allowing to transport music everywhere: Increased exchange between artists, a lot of new inspiration for others
-Wealth and culture (a lot due to the new media in latter case) made music very popular for everyone, a lot of bands came into existence, short tracks of not much more than three or four minutes replaced the old, complex music, a lot of experiments with different musical instruments were made and exchanged by media. Also, new technology (electronic instruments or, later, purely electronic sounds)
As the century ended, there just wasn't any "big thing" left to discover, all the huge discoveries have been made already.
However, I think there was a big developement in the last decade. International stars became less important than ever, music is more and more individual. Existing styles varified and spread into countless new substyles, some bands and musicians effectively create a new genre with every new album they create.
And thus my opinion is that it's a very individual decision how to rate the latest decade in terms of music. Some people might've found a lot of new niche music which they love, whiler others miss great overall developements (which, I think, won't really happen any time soon - if ever again at all).
For me it was a great decade. I don't miss the big names and found many likeable subgenres, bands and DJs.