From the B-net store page for Halo 2 (Xbox)
Features:
Master Chief can now wield two weapons at once, board Covenant vehicles and steal Covenant weapons like the incredible double energy sword
Immense single-player action with maassive landscapes and huge cities to explore and defend - destructible and interactive environments
Take the action online with your Xbox Live and switch sides, to become a Covenant Elite!
As I recall, there was no such thing as a "double" energy sword, no destructible areas, and you could only play as the Arbiter in campaign, not in matchmaking. So whats that about?
Also spelling error in official feature list, lol.