As I understand it, they have cleaned up the hangar matte painting, fixed a continuity error:
Near the end when Ripley is on the dropship, she is seen arming herself. We see her grab a flamethrower from the weapons rack. She then lays a pulse rifle on the deck. Next she pulls a pulse rifle from the rack, and lays down a flamethrower. (The 2010 Blu-ray is slightly re-edited to remove this error.)
Who knows what else...