Here are my impressions from the two hours I've played. I've gotten two of the achievements so far:
-When you get to the area of the DLC sidequest, you first have to help a group of brotherhood outcasts fight off some super mutants. Then you follow them into their base.
-Once you're in the simulator, you have to infiltrate a Chinese base solo. You lose all your stuff, like Tranquility Lane. You're given a silenced 10mm pistol, a knife, a stealth boy, and apparel. The guy with you says you have the option of going stealth or guns blazing. I went stealth until I met up with him again, even after I picked up a Chinese assault rifle.
-After that, you destroy some Chinese weaponry. When you're done, it brings you to the US base for a debriefing. That's where I stopped.
-It's all combat. You fight tons of Chinese soldiers. You also fight some invisible ninjas who remind me of Raiden from MGS4.
-When enemies die, they evaporate, preventing you from searching their corpses.
-You can't pick up as many items laying around as you can in the main game. I'm not sure you can pick up anything non-weaponry actually. For example, I saw a pile of metal scrap, but couldn't pick it up.
-There are red glowing health and ammo re-generators as you go along. They refill both completely and you can use them infinitely. They also seem to always have weapons, grenades and mines next to them.
-It's super linear so far, reminds me of a FPS more then the rest of the game. There are a few side areas to explore, but not a lot.
So far I like it, but I'm curious where the story is going.
EDIT: I remember now that you can pick up holotapes to listen to.