Gamespot played the first 90mins of Phantom Liberty and gave their feedback as to what they experienced. The video is below but here is bullet points of the main items they discuss. SPOILERS AHEAD;
 

• Made the point while Dogtown is part of Pacifica it is "tough to get in and out" as in the start of the story you sneak in. Hence where the facemask disguise comes in? That said makes me think you are more or less trapped in Dogtown for the majority of the expansion.
• You resuce the President within the first few missions and she asked you to go find Reed, hence how he gets involved.
• I was correct in my trailer breakdown, Reed is a undercover op working in Night City for the NUSA.
• They have added branches in these new missions, they said it is possible to piss Reed off to the point where he won't help you for example.
• There is a lot of flavor dialog with Silverhand that fleshes out new parts of his background.
• CDPR was cagey about how much this story will influence the main story. It's implied it will be about the same level as Hearts of Stone for Witcher 3.
• CDPR also dodged questions about if this will affect the main story endings.
• Also, CDPR stated EVERY game system in the base game has been touched. Either edited, added to or fully re-written. This includes the new police system they confirmed is in the expansion.
• Health, armor, combat damage and skills have been redone.
• Cyberware has limits now depending on your level/stats. If you add more cyberware than your body/level can handle they actually cause a debuff rather than a bonus to your stats.