Halo 3: Excellence abound.
Halo 3's campaign is very short. Unacceptably short on easy, but acceptable on heroic+. But that's not to say it is bad. The campaign is ridiculously streamlined from start to finish, with an unprecedented level of polish rarely seen. Graphically it is superb, but not amazing. By no means amazing. Havok physics are incredible, and the bloom/HDR effects look great, but the textures and models don't compete with games like Gears and COD4.
4 player co-op is amazing, and tons of fun. Forge is revolutionary and gives users the power to create wonders. Saved films and screenshots are great for saving those ridiculous good times you'll have with friends. But these seem like bonuses, and although they come together nicely, individually they aren't game-breaking or game-saving.
Multiplayer
This is where the game truly shines. Put Halo 2's multiplayer with a new twist (equipment), add great new maps, vehicles, weapons, and grenades, and make it lag free and in a thriving community, then you've got Halo 3's multiplayer. Do I need to say more than that?
The community isn't up to standard sadly. Unless you play with actual friends or are in a party and competing seriously, don't expect any practical use of the headphones. Kids constantly yell and scream when they are killed. They will betray you. They will sing and annoy you to pieces. But only sometimes. Thus is why I took off the half-merit.
Consensus
+ Great streamling campaign
+ Amazing mutliplayer you'll keep coming back to
+ Forge, theater, co-op, are great
- Very short campaign
- Less than ideal community... sometimes
4 and a half stars out of five.