Halo3

 This might sound biased but I'm a Halo fan. Before you go off and grab the pitch forks hear me out. I had my doubt about Halo 3 after the disappointment of Halo 2. I was one of those people who early on said that Halo 3 was going to stink and that it was going to fail etc. But boy was I wrong! I don't want to make this as huge review but I'll do my best.
The story follows super solider John aka Master Chief aka Spartan 117. When you left off at Halo 2 Chief was on an forerunner ship headed to earth on his conquest to rid the galaxy of a hostile alien race known as the covenant and now he want to continue his crusade and save his trusty AI sidekick Cortana from the zombie like Flood. Basically this game ties up the Halo story in one of the best story telling in a game period, only Mass Effect and Assassins Creed can hold their own compared to Halo 3. The voice acting is some of the best ever recorded and will never stop amazing you.
The game play is very similar but tweaked none the less to the other halo games and first-person shooters. You have your share of futuristic weapons and human lead shooters none the less. The game play is similar yet changes over the levels, in one level you are in a warthog (jeep) almost the entire time and in another you are blasting away alien ships with a tank, to keeping your sniper rile handy and battle rifle busy in another.
No matter what you hear Halo 3 is a stunner. The water and light effect are astounding and the character animations are incredible. The AI of the enemy is one of the best parts, they are relentless and brutal especially when you bump up the difficulty. The friendly AI is almost brain dead but they get by. The forge, a map maker to your own imagination, is great to do what you wish with any multiplayer map.
The XBOX LIVE is by far one of the best aspects, there is so much to do. I don't want to go into details other wise this review will be 10 pages long, it is the best online play ever created and is only matched by Call of Duty 4 but I think Halo 3 wins over all, the connectivity is better and less lag rather than COD4 which has amazing online play but lacks better internet connectivity.
Over all Halo 3 is incredible. Any fan to Halo or Sci-Fi shooter will love halo 3. Don't listen to one to three star reviewers and forum bashers who say that Halo 3 is not a good game. Those people obviously over estimated one the best games of the new millennium.