Turbine's official The Lord of the Rings Online: Shadows of Angmar website has been updated with some preliminary information about class-specific traits players will have access to in the game.
The most basic Traits do fairly simple things like increasing your Might stat or your block rate in combat. These Traits take a number on your character and make it bigger. Simple, but effective, these basic Traits are the first ones you will see throughout the course of your character's advancement.
More complex are the Traits that modify skills (or groups of skills). For example, one Trait may add a new effect on a critical hit that it didn't have before, while another may make a skill uninterruptible or reduce the power cost of an entire group of skills. Yet another type of Trait works only after a specific combat event, allowing you to gain power on a critical hit or increase your defense on a successful block.