Just not enough to be a masterpiece
The game starts like you would imagine Master Chief coming back to earth to "Finish The Fight" fighting off waves of Brute, Grunt and Hunter attacks. The story is your basic Man Vs. Alien affair, however Bungie have done well with wrapping up some ends to this the game. Filling in plot details, etc. This is set to be continued in a spin-off comic series.
While the missions do well to wrap up the story a little more fleshing out wouldn't of hurt it, maybe longer levels to give more of a backstory. Unfortunately, this game suffers in length only 9 missions to finish what began back in 2001, i know it might of dragged on, but surely one or two more missions couldn't have hurt.
The graphics are basically Halo 2 in HD with the lighting having the only noticable uplift from last-gen. Don't get me wrong the graphics are good, just not that good. I fell that BUngie have used a lesser powerful graphics engine, so they can produce many enemies on screen at one time and there are a lot of enemies, which makes for some challenging gameplay on Heroic or Legendary, but thats obvious really.
Where Halo 3 stands out above everything else is, of course, multiplayer this is the shining jewel in Halo's crown. Even if it is still halo 2 with new features the multiplayer alone is worth buying the game for, thats without mentioning Forge or 2-4 player Co-op over Live or System Link. With the multiplayer you can have your standard deathmatches or various other types of game settings (CTF, Infection, Team Slayer, Etc) which all make for perfectly balanced and always-fun-to-play multiplayer matchmaking.
Forge is an in-depth editing tool for you to create custom scenario's or make a wacky level for yor friends to enjoy, just yesterday i lifted the elephant from placing a tank inside the back of it and lifting it up. You can then upload these to bungie's service which can be given to people for download to use time and time again.
Halo 3 is an outstanding game in the FPS Genre and deserves nothing but praise for what it does, however a longer campaign and better graphics may have helped to make this the perfect FPS for the year.