From the company website

Arcanum Heroes is the newest expansion for the Arcanum game system. Six new heroes wait for you to play, the vile Dark Mage, the Orc, the Seer and the Halfling are but a few of the new characters you can play with this expansion. Take a walk on the dark side and seek the evil lore of the Dark Mage, or sneak about the shadows seeking gold and glory as the Gnome.

Fully compatible with all the other Arcanum expansions, you will find this just adds more fun and options to the already fun mix.