Halo 3 is an interesting mix of established protocol and intriguing new stuff. For example, the gameplay doesn't stray too far from Halo 2, which, in turn, didn't exactly reinvent the original Halo. Don't take that as a negative, because it means that Halo 3 plays extremely well, with the same types of light tactical considerations that have made the series stand apart from other, faster-paced shooters. The balance between your guns, your grenades, and your melee attack has always given Halo a unique feel in the genre, and those same considerations apply today, both in the campaign mode and in multiplayer. You'll also have new weapons and items to consider, such as a host of Brute weapons. One example is the spiker, which is an exciting automatic pistol that fires quickly and decimates opponents, especially if you're holding a pair of them. Another is the mauler, which is a one-handed shotgun that can level enemies up close. You'll even find weapons so huge that your movement speed slows when you carry them. When you use these weapons, the camera pulls out to a third-person perspective so you can see your missile pod, plasma cannon, or flamethrower as it fires. And then there's the gravity hammer. Originally shown in Halo 2 (where it wasn't usable by the player), the gravity hammer is a large melee weapon that will wipe out most regular enemies in one swipe. Needless to say, it can be especially fun in multiplayer settings. The end result is gameplay that feels wholly familiar without retreading the same ground too heavily.
The campaign is structured in much the same way as past Halo games, with multiple chapters and effective streaming that ensures you'll see load times only between chapters. There are also lengthy vehicle sequences to break up the on-foot action. You'll pilot the classic Halo vehicles, such as the Ghost, a hovering one-person craft that's fast and deadly, and the Warthog, a dune buggy with a turret mounted in the back. You'll also see new vehicles, such as the Brute Prowler, which is a two-person vehicle with turrets. Like in previous games, the vehicles are fun to use. Also similar to previous games, the artificial intelligence can't drive very well, so if you're playing alone, you'll usually want to grab the steering wheel rather than the weapons.
Source : GameSpot