Rogues are most successful when their deeds never come to light. Fond of poisons and silent projectile weapons, rogues rely on a blend of stealth and minor mysticism.
Rogues work best as backup to the main tank (Paladin or Warrior) within a group and can apply quick damage with skills such as Ambush and Garrot before her target has had chance to land a single blow. They are able to effectively put humanoid mobs to sleep with Sap to help take the heat off a situation and they are not bad pullers either. Good for thinning the crowd if your party is outnumbered.
With Stealth and Vanish skills they are able to scout out situations in order to assess the lay of the land and report back to the party to prepare attack strategies. These two skills are useful for slipping past a mob you don't wish to fight and you can even activate Sprint whilst in stealth.