The new skills alone are worth the price of the expansion. Without naming them all, I'll mention a few of the cooler new perks. Thieves can now do a crippling strike, which has nasty effects on bad guys depending on the thief's level. Rangers can now track, which basically tells what types of creatures are in the area. Druids gain the ability to shape change into animals and elementals.
Bards gain a lot of new songs, which have varying effects.
The new spells are pretty nice too. I won't mention them all, but to give you an idea what to expect, check below. 3d8 damage to all living creatures within a 10-foot radius. Any creature that dies this way is transformed into a 3 hit die skeleton under the control of the caster. This spell enables a priest to aid and protect any one being other than himself.