This actually ranking best shooter in my book...
The graphics aren't as good as some are today, but for the launch of the Xbox, they were superb. If you reach some parts in levels, you would really see that environments and all such are complete masterpieces.
The sounds are completely awesome. The solid bark of the M6D pistol, to the extremely satisfying chatter of the Assault Rifle. The heavy sound from the roar of the Warthog... All topped by the incredible soundtrack by Marty O'Donnell. Love the action and drumruns during significant parts like the Silent Cartographer beach invasion.
Multiplayer is meant for more grand scale battles with System Link, not small 1v1 free for alls. But let's face it, once you've played Halo on a LAN, you won't want to go back to a simple 2 player game ever again. After a friend of mine hosted a LAN, the first anyone had ever been to, it was like a new kind of Utopia. It was fresh meat for me to slaughter.
Halo is one of a kind. It will make you seek blood, it will make you freaked out, it will utterly amaze you. It's a masterpiece and an instant classic at the same time. Check Mario. Buy it, and that's an order, soldier!