Ewwwwwwwwwwwww, all the power armor in Fallout 3 sucked... Except the helmets for T-45d (Brotherhood Power Armor), and the Winterized T-51b. It just wasn't bulky enough, power armor is supposed to make you look and feel like a tank.
I'm pretty sure there won't be any Enclave, at least not as a main Antagonist this time around. They've been the baddies for two games already and they're extremely weak as of now.
And Karma is still going to be there, but it won't effect how people see you. They can still see you as a savior if you butcher people and eat them and no-one else knows about it. It's just a measure of how much of a bastard you are.
There are also no straight antagonists either, there are more grey areas as the two main factions are joinable and for their respective questlines I would assume you either destroy or severely hamper the other.