I am a huge fan of the Halo series, I have been playing it ever since Combat Evolved was released in 2001.  Halo has literally the most compelling story ever in the history of gaming, books, magazines, graphic novels, and even movies have been made dedicated to this series.  So as for Halo 3?  This is the icing on the cake; coupling beautiful graphics with insane gameplay and the most interesting science fiction story in a game EVER.  Let's start with campaign:  Halo 3's campaign offers a diverse array of Weapons, as well as a variety of vehicles and units.  Unfortunately I do not have time to finish this tonight, so I'll continue after work tomorrow.