Basically , they are really four:
1- You receive a Defence value bonus according to the character level in each class .
2- The base classes' maximum level is now 10 (and you receive new class ablities almost each level)
3- Some skills are amalgamated (hearing and vision checks are made with a single skill: Notoce) , and other separated (specially the technical ones)
4- There are new base classes : the Ranger , the Trader , and the Worker (performer) .
there are a few more (specially the vehicle/spaceship combat rules) , but these are really the most important .