Quickblitz of some highlights for you.
On a technical front, the game's overall playability and stability have been improved. For most people, the stuttering issues have been mitigated or killed off to a great degree. AI is steadily improving.
New ships, three of them; while two of them are nominally the same ship, they're different models, both actual-model-wise and operationally.
Powerplay. You'll have to read up on that one yourself, there's a lot to cover. YMMV should be your mantra while checking it out. Even if you don't sign up, it will have some impact on your game as the Powers do their thing. Remember that you can take advantage of some regional effects without actually joining anyone.