There are a lot of things that make Halo 3 stand out from other shooters, in addition to a great single player campaign you have the option of four player co-op, a deep and enjoyable multiplayer experience, the ability to create video clips of past games (single player and multiplayer), and a level editor.
The graphics look stunning and colorful (a rare trait for current gen shooters), and the sound is on par with the overall presentation. It may take a while to notice what makes this game look different from Halo 2 but apart from a few dodgy character models, this game is one fine looking thing.
The single player campaign is once again too short and is infamous for one of if not the worst level in the series. That being said the rest of the levels are stunning to look at, they are very linear but very diverse and interesting. If you have played and completed the first two Halo games then DO NOT play this one on the normal difficulty setting. The game is way too easy on anything below the Hard difficulty and as a result you really do miss out on a lot of great scenarios which require you to think rather than run and gun all the time.
Of course the multiplayer is what keeps the life in this game, there are so many different modes for this game, you can play the campaign with three friends (or strangers), and you can play it like the normal campaign or like an arcade game racking up points for kills. Skulls, which are like easter eggs hidden around the campaign levels allow you to make a number of changes, from making the game more challenging with stronger enemy's, to grunts that shoot out confetti when shot.
All the classic multiplayer games are here as well along with some new ones and these games can have you online for months at a time. You can customize your character's armor and make you own emblem, you upgrade your rank for different accomplishments depending on your game type and all these things as well as forge and creating video clips and stills of your finest moments pump so much extra life into what is already a great addictive experience.
A great game which you will easily get your moneys worth out of