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!
These are maps made by reus with CEA sounds, models, weapons with AI bots battles so also you need halo editing kit to rename the maps to make them named like this red_vs_blue_2 with the dashes in between because the original maps have spaces and wont load due to the spaces so you need to rename them with the dashes. enjoy :D