With only four classes for each of its two factions, BioWare's Star Wars: Knights of the Old Republic further mixes things up with the Advanced Class system, a talent system that splits each class right down the middle.
The Advance Class system comes into play once your character in The Old Republic grows in power. Upon reaching that point, players will be able to select between two advanced classes, further honing their role in the MMO world.
For instance, one Sith Warrior Advanced Class will focus on charging in and taking the brunt of the damage, or 'tanking,' while the second will focus on doing as much damage as possibly, taking foes down quickly, known in MMO circles as the DPS (damage per second) role.
Choosing one Advanced Class or the other will lock players out from skills from the alternative Advanced Class, though a shared skill set will be available, featuring skills both of the more advanced roles can use.
It's basically a talent system like the one you see in World of Warcraft, with fewer choices involved. You won't need to worry about mixed talent builds or swapping talents depending on the situation. It's all about defining who you're going to be in Star Wars: The Old Republic.
Advanced Classes Overview [Star Wars: The Old Republic]