Though the guitar-based infusions of Steve Vai's backing work made for maximum badassery in Halo 2, we're still partial to the minimalist, haunting quality of the original game's theme tune, which begins with chanting before branching off to become a triumphant tune that really makes you want to kick some Covenant behind. It's an extremely original theme that avoids the noisy bombast that first-person-shooter games are often known for, instead making the most of its Gregorian chant to class things up a little, while still having time for something a little livelier later on. This theme has proven so popular that it's appeared in every Halo game since in some form - with or without kick-ass guitar work from Steve Vai - but always retaining that signature chant above all else.