The way Energy Resistance works has changed. It now applies against each individual attack, like DR.
In 3.0, it would just absorb a certain amount of damage per round, so that it was possible to overwhelm it if you did enough attacks:
i.e. A creature with Fire Resistance 20
-- In 3.0, you could cast two fireballs on the creature, each doing 30 points of fire damage. It prevent the first 20 points from the first fireball, and nothing from the second. The creature would take 40 points of damage.
-- In 3.5, you cast two fireballs on the creature, each doing 30 points of damage. It prevents the first 20 points of damge from each fireball. The creature takes 20 points of damage.
This is a pretty big change.
In 3.0, it would just absorb a certain amount of damage per round, so that it was possible to overwhelm it if you did enough attacks:
i.e. A creature with Fire Resistance 20
-- In 3.0, you could cast two fireballs on the creature, each doing 30 points of fire damage. It prevent the first 20 points from the first fireball, and nothing from the second. The creature would take 40 points of damage.
-- In 3.5, you cast two fireballs on the creature, each doing 30 points of damage. It prevents the first 20 points of damge from each fireball. The creature takes 20 points of damage.
This is a pretty big change.