This game may not be a perfect 10, but it is still plenty fun both online and off.
The story in Halo 3 picks up right where Halo 2 left off. The evil covenant guys are on their way to earth while gearing up the Halos which are gigantic weapons that will destroy all life in the universe. Awesome. Naturally, everyone in the game expects you to do everything yourself. Again, awesome. You will play through 9 missions (the first playthrough will probably take you between 10-15 hours) which, despite the previous games, somehow dont feel repetitive. It is pretty amazing, but this game actually managed to not seem repetitive, which is surprising to me. The guns are fun to use, the enemies are challenging to defeat and the levels are well-designed. It's pretty awesome.
However, the single player isnt without faults. There are parts of the single player campaign that just seem annoying. For instance, in mission 2 near the end, there is a bomb going off and you need to escape from a building. Well, it makes the lights go off for a few seconds and your controller rumble like crazy every so often. It's atmospheric the first or second time, but after that, it can get on your nerves. Furthermore, it can sometimes seem like the game is just throwing enemies at you. In most games, it seems as though enemies will logically be in your path, however in Halo 3 it can seem like the enemies are just lengthening the game in some areas. Halo fans will probably bash me for that, but I couldnt care less.
Now, the online in Halo is a bit of a wild card. It can be fun, certainly, but it can also be incredibly annoying. When its fun, you will want to play it for a while. The action is fast paced, there are good mechanics to keep out TKers and the levels work well for multiplayer. However, there are several factors that can make your gameplay experience extremely aggravating. The first of these factors is the other players. It's really annoying when a 9 year old kid decides to leave his mic turned on so you can hear every little thing he says. And trust me, little kids love to scream. Either when they get killed, or when they run into an enemy they didnt expect, or whatever, they just like to scream. It gets annoying. There is a mute function, but come on, I shouldnt have to use it THIS often!
The next factor is some annoying game types. For instance, Team Rockets. Now, with a group of close friends, Team Rockets would probably be really really fun. When you are planning with a bunch of random people, Team Rockets is really annoying. Shooting your team mates is easy (they love to jump in your way to KS you) and since they can choose to kick you for one offense, it can really mar your game experience. Furthermore, leaving a game with annoying kids or an annoying game type will result in a loss of experience. So basically, you are prevented from leaving a game, that is poor due to no fault of your own, because Bungie basically locked you in. Great, that really helps the gameplay experience.
For whatever faults the game may have, Halo 3 is still an amazing shooter. The graphics are good, the gameplay is fun in both the campaign and online (mostly in both cases) but it isnt perfect. Perhaps in future games in the series, they will get closer to perfection, but for now, this game is just a great shooter, that most 360 fans should definately pick up (if you are a 9 year old kid, or in that approximate age range, and you like to scream into your mic, please refrain to getting this game).