The Halo 2 map pack is a collection of nine brand new maps. In addition, upon downloading the power of the frag grenades, melee attacks and brute shot has all been increased. New cinematics that tie in with Halo 2's story and the E3 Halo trailer can also be watched.
The new maps are even better than the old ones. More attention has been given to the textures and lighting within each map and certain means of cheating such as grabbing the flag through walls has been eliminated.
8 months after its release and Halo 2 is still the most fun to be had online.