There's a large war going on outside, and you're part of it.
Tabula Rasa has changed a bit over the past year. Gone is the purely instanced-based gameplay with sleek technological dungeons; in enters a persistent oustide combat zone. This is where it seems most of the game will take place, with a few exceptions for those missions that require very few people present. This zone still has missions within it, however--the battle is ever-raging. Your actions will actually affect the layout of the zone. When humans capture certain towers, it means that your drop ships can now go there, providing more NPC reinforcements and thus making it easier to maintain control of the area.
The one thing not mentioned, however, was what the point of maintaining the area was. The NCSoft representive did say that it'd be nigh impossible to control the whole area. He also mentioned that there will patches with changes to the warzone over time, to reflect the fact that you should be getting more and more ground under human control.
What is it with aliens and 4 legged insect looking machines?
The story itself hasn't changed much. There's still a benevolent race of aliens who befriend the last free humans and give them special powers and then send them into battle with the Bane. The Bane, of course, are a threat to the whole galaxy. Now, it was mentioned that you should meet some of the benevolent aliens through the course of the story, and perhaps the fact that they're making you do their dirty work may be explained.
Overall, the combat system is still very similar to how it was last year. It's largely gun-based combat with several weapons like machine guns, rocket launchers, and pulse rifles. You also get a healing item that never runs out. Finally, you also have the alien taught special psychic powers. These can launch nice area of effect attacks, or long distance force like pushes.
The changes seem to make the game feel more persistent, and lend more weight to your actions. But it remains to be seen if the missions and story will make participating in an unending conflict something you want to spend your spare time doing.