Primary Features:
Two new Archmage style classes; Arcanist and Elementist.
One new Enchanter class.
Some extra talents for Alchemist.
Lots of new artifacts.
Artifact gems are more interesting to attach to golems.
Crystal Focus/Heart items can be deconstructed to recover the gem.
Angolwen Academy: Get training in the Arcane here.
3 new runes.
Two new item types with unique egos: Ritual Blades and Wardstones.

Arcanist Features:
Like Archmage, but also starts with temporal, meta and nightfall unlocked, and no elemental categories.
Has two unique categories; High magic and Void magic.
Can also unlock Illusion, Distortion, Power and Morph.

Elementist Features:
Like Archmage, but only elemental categories.
Has three unique categories; Elementalism, Corrupted Elements and Elemental Fusion.

Enchanter Features:
Apply a variety of enchantments to your equipment.
Dabble in safe and unsafe hedge magic.
Defeat monsters with your prowess with a staff.

Archmage Features:
1 new category containing 8 arcane/elemental combo spells.

Alchemist Features:
Altered Alchemists Guild quest.
Two new unique categories: Poison Alchemy and Metal Alchemy.
They also get access to Mana Alchemy and Herbalism.