Awesome multi-player. Okay campaign.
Multi-player on the other hand is the best yet of the Halo-trilogy. With the newly added tools such as the tripmine, radar jammer, deployable shield, deployable grav-lift, and of course the always helpful bubble shield. The new weapons have also become some of the new favorites, such as: the mauler (in which if dual-wielded is equivalent to the shotgun), spartan laser (in which the shooter awarded with a medal for each kill), and the missile pod (basically the new rocket launcher, just not quite as powerful) are just some of the many new weapons in Halo 3. But of course most Halo fans prefer to stick to the classic battle rifle as much as possible.
The maps are for the most part amazing too most all who play, and with new maps coming out frequently, bungie is doing a great job at keeping the Halo fans on their toes, excited, and interested and addicted to the game.