Armor Proficiency (medium)

Obsidian has not stated if armor proficiency (medium) will be included in NWN2, however it is core to the combat mechanics.

Armor proficiency (medium)
Type: General

Benefit: When you wear a type of armor with which you are proficient, the armor check penalty for that armor applies only to balance, climb, escape artist, hide, jump, move silently, sleight of hand, and tumble skill checks.

Normal: A character who is wearing armor with which she is not proficient applies its armor check penalty to attack rolls and to all skill checks that involve moving, including ride.

Special: Fighters, barbarians, paladins, clerics, druids, arcane archers, blackguards, dwarven defenders and pale masters automatically have armor proficiency (medium) as a bonus feat. They need not select it.

NWN comparison

 * A character in NWN who did not have the correct armor proficiency could not wear the associated armors at all.