Here are some questions and answers that i found at
www.bungie.net .
Q What new weapons will be available in Halo 2?
A So far there have a been a few new weapons revealed. The Battle Rifle is an evolved version of the original assault rifle and features increased accuracy, a scope, and a slower rate of fire. The SMG (Sub Machine Gun) is a rapid-fire gun that trades a high volume of bullets for decreased accuracy.
Of course these are others, but we can't tell you about them yet.
Q What are the new Covenant races?
A The Brute has been described as a cross between a gorilla and a rhino and will be a serious force to reckon with on the battlefield. The Prophets have been referred to as "giant space popes" and they provide the political, religious and spiritual leadership in the Covenant.
As for the others... you'll just have to wait and see.
Q Will flying vehicles be available in multiplayer games?
A You better believe it!
Q Will Halo 2 support online play via Xbox Live?
A Absolutely! Forget everything you know about Xbox Live. We intend for Halo 2 to become the definitive Xbox Live experience with well designed and extremely robust support for online play. We'll have much more to say on this subject in the months ahead.
Q What multiplayer game types will be offered in Halo 2?
A All of Halo's multiplayer modes will return including Oddball, Race, Slayer, CTF, etc.. In addition to these classics, we have some big plans for Live that we'll reveal a little later.
These are some of the questions, there is still many other questions but these are the best.