Halo 3 is an action-adventure shooter that puts you into the hands of the Master Chief, who is the last Spartan II left to save the Earth. The Elites have discovered the truth behind the Halo rings and now race along side the humans to stop the Covenant and The Prophet of Truth from lighting the rings, which if done would mean the end of the universe.
This game is fun in many different ways. You could work on beating the campaign on Legendary, which is known for its near impossibility to beat without dying at least a few time, or you can go online and pit your skills against people all around the globe (although you probably will only play with people in nearby countries due to separate servers).
Now a few main things that make this different from Halo 2, as most of you have already figured out. One is the ability to play campaign online (HOLY CRAP FINALLY). This mode is fun in all difficulties and for all reasons, whether you want to compete against each other for points or kills or if you just want to "finish the fight" and find out what happens in the end.
Also, now there are two "levels" of skill now. One is experience, where you level by ranks found in the US army (although it is strange because the soldiers in the game are Marines and therefore should use the Navy ranking system) and the other is through skill, labeled with number ranks. To get experience, you have to battle and play a lot of games, although you would get more points for winning than losing, its just experience that counts. To get higher levels, play one or more playlists constantly and keep winning. Currently the highest number level is 50 and the highest rank is General.
One thing you will really notice (and I mean NOTICE) is that the weapons and vehicles are slightly different now. The sniper rifle now shoots slower and has a moderate amount of recoil, which means you actually have to have some sort of skill when using it. Also, due to the game miscalculating the "lagtime" of the shots, you may actually get a headshot on the enemy; however, it may not register and the enemy will take no damage. No worries, because you still have another chance to take him/her out. Also, the battle rifle shoots slightly slower, the SMG does less damage but has a higher firing rate, the brute shot does less damage, the shotgun does MORE damage, and the sword is not as fluid as it has in Halo 2 due to the new battling system that's been inputed whenever two swords ever come into contact with each other. The warthog drives slower, the ghost is stronger, and the turret on the Scorpion is now operated by a different person, and although the wraith never had the tureet in multiplayer before, it can also be operated by another person now.
New weapons and vehicles have also been added. The brute spiker is a stronger version of the SMG but fires slower and is almost completely worthless. The Assualt Rifle from Halo 1 has a smaller range of fire but also has a smaller clip. The Brute Mauler (or NOOB CANNON as its referred as) is a smaller dual-wieldable version of the shotgun that packs a serious punch UP CLOSE, and I mean UP CLOSE. The Spartan laser is a kickass weapon that shoots 3 high beam lasers simultaneously after charging for 3 seconds. It can be used as a sniper or a vehicle killing, but unless you have some serious skills or luck, I'd suggest keeping a short range weapon with you for up close encounters. The Brute Chopper, anooying as it is, is a motorcycle with grenade launchers, so take it out fast before it kills you. The Mongoose is a cut down version of the Warthog and looks like an ATV. Unless you have some serious skills with driving, i would only recommend you use this vehicle when moving fast to plant a bomb or taking a flag. And how can I forget the Elephant? Its the ultimate indestructable vehicle used on Sandtrap to get flags or planting bomb. It has a s#&*load of detachable turrets and where the mongoose spawns in multiplayer games.
There are new maps, but I wont go into detail about them. Theyre all fun to play on and just play on them alright?
Some major glitches have been taken out of the game. Superbouncing, which involved a specific procedure to jump really really high above the level, has been taken out. The BXR, BXB, YYB, all forms of Sword cancelling, and any other form of button combos have been taken out; although oddly the gun may reloads by itself when you try to melee a result of the new changes to fix those glitches. Tank Flipping (Whether with a scorpion and a wraith or with two scorpions) has NOT been taken out of the game, but it may be harder to do them. There were other glitches but I don't really remember them.
The last thing I would like to address is the ability to change the appearance of your character or any of the levels. You have the ability to customize your character using colors and different armors that you unlock through achievements in matchmaking or in campaign. Using Forge you can create your own levels to play with the help of your friends to create new gametypes and have hours of fun.
This review has turned out to be pretty long, so I'm going to close it by saying that if you buy this game, you will have hours of fun and play for a while before you switch to a different game. So go on and play already ( and if you dont have it, go BUY IT) and good luck.