It's a little from column A and a bit from column B.
There are still some restrictions.
There are 4 Force using advanced classes (I'll use Imperial Classes): Juggernaut, Marauder, Sorcerer and Assassin and 4 "Tech" using advanced classes: Sniper, Operative, Mercenary and Powertech.
The two Force using jobs (Sith Warrior and Sith Inquisitor) can be any force using advanced class now. So a Sith Warrior, playng through the Sith Warrior story, can now be single saber wielding, ranged attacker or healer (Sorceror game play) and a Sith Inquisitor, playing through the Sith Inquisitor story, can be a dual wielding melee fighter (Marauder game play).
The two Tech jobs (Imperial Agent and Bounty Hunter) can be any tech using advanced class. So an Imperial Agent, playing through the Agent story, can dual wield pistols (Mercenary game play) and a Bounty Hunter can wield a Sniper rifle (Sniper game play).
There's no change to the game play of the advanced class you choose. A Bounty Hunter wielding a sniper rifle will play exactly like a Sniper does now, you'll just be doing it AS a Bounty Hunter, playing through the Bounty Hunter story.
Also @
Darththeo covered it too.