Brilliant - Master Chief back with a bang!
I quickly completed the campaign on Normal to finish the story but without being challenged too much. The story was brilliant and I really got immersed in it which is something that hasn't happened in a game since MGS, MGS2 and MGS3. The story finishes with a bang without the disappointment of 2 which leaves you with a better feeling.
I then started on the multiplayer which again was superb. They have all the good old multiplayer games and a few new ones thrown in for good measure. I really grew to love this side of the game and as a consequence still haven't finished the campaign on Legendary!
However I think the best aspect of Halo 3 is the Forge part. I didn't really know what it was about 1st of all but then me and a couple of friends really got into it and it started to overtake the multiplayer. I really would recommend players getting into the Forge section as it is highly addictive.
Overall I think Halo 3 is the best in the series and Bungie really pulled out all the stops with this game which is up among the top titles on the Xbox 360.