To me Halo, includes every element of the series. The UNSC, Covenant, The Flood, Spartans, Elites, etc all make it Halo as I see. And of course I can't forget the mysterious Forerunner Architecture and the TRUE history behind the Forerunners (Not Greg Bear's copypasta nonsense).

If Halo 4 has bad music, I don't know, I might actually play it once for the campaign or multiplayer and shelve it. If a game doesn't have good music and audio, then it's not worth playing beyond the "I played it" reason. Marty O'Donnell and Michael Salvatori did an awesome job with Halo 2, 3, ODST, and Reach. I expect it not to be as good as theirs, but I still expect it to be good.