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 is the mission assault on the control room but its modified to make it look like a mission that your fighting on earth, contains NMPD biped tags, SWAT biped tags, halo reach marine and covenant biped tags and halo 3 and reach weapon tags, put the map file in your halo custom edition "maps" folder and type in console map_name b40, enjoy :D