The game of the decade, and you know it! The first-person shooter that gave a breakthrough and is at the top even today!
Campaign: With the difficulty modes Easy, Normal, Heroic and Legendary you can replay the campaign in your type of difficulty. It is a quite good campaign but the only downside is that it should had have a little more unique terrains and missions but it's barely unoticable and if you have not played all the games a million times. Walk with Arbiter next that should have been more active AI when playing alone. The new equipment in the game sure made it better and the campaign will never get boring (if you really are in to the Halo storie).
Gameplay (Multiplayer): This is the best made multiplayer shooter in my opinion known to man (for know). They are alot of playlists were you can play the diffrent gametypes like Slayer, oddball, infection. But also to make the people enjoy multiplayer even better Bungie (the game developers) added a special system which calculates your skill with the others and chooses the most even games. Ranks from Recruit-Five Star General are also in the multiplayer feature and are waiting for you to earn. Clearly this game's multiplayer is one of a kind.
Forge: It's a editor mode for every player (not to only those programmers to modify maps) which lets you edit maps by deleting, adding or move around object and save your samples and share it with your friends. "Live they way you like" is a way you can explain forge quickly.
Theater: A simple rewatch feature added to the game that allowes everyone to rewatch their battles from campaign to multiplayer and see "what hit ya".