HALO is one FPS that really did introduce many new gameplay elements. It offers all that is said below and the modifications already in development look to refine and improve the "HALO experience" even more!
This a map where you play as an elite and fight a bunch of brutes, grunts and jackals and this adds halo 3 assets and sounds, weapons as well as music, place the map in your halo custom edition "maps" folder then type in devmode console map_name covenant-rebellion, enjoy :D