Before I write this, the CoN: RtA in Off Topic has some of the same things but there is more in thi one.

1) Choose sides: Good or Evil
2) New level cap: 80
3) Depending on the side you choose, you go to different locations on the planes.
4) Two new races: Vah Shir Berserker and Iksar Shaman
5) Some of the new enemies include ogres and dragons.
6) 3-4 new spells for each class:

RANGER
Light Quiver - Reduses arrow weight
Summon Arrows - Summons an amount of arrows

WARRIOR
Natural Resistance - Lowers the amount of damage taken by magic attacks

CLERICS
Mark of Retribution - Health boost after each successful attack

WIZARD
Wave of Flame - Injures monsters within a certain radius of flame

SHADOWKNIGHT
Shadow Step - Instantly puts the SK in a safe place

VAH SHIR BERSERKER
- Throwing weapon skill
Summon Axes - Like the Ranger's summon arrows, but instead, axes
Berserkers Rage (Passive)- Temporary buffer against your enemies when your health fall below 25%

IKSAR SHAMAN
Summon Badger- Summons a badger to fight with you.
Pus Storm- Like Wizards Ice Storm and Fire storm, causes large globs of pus to fall on your enemies.
Giant Growth- Causes your Iskar to become larger, and attack for more damage.