Mind you, they changed almost everything about the game. They changed every rules system. The conversation wheel remained the same, but almost everything else is different. I'm guessing that the tactic of "max out one weapon" is out. Heat buildup is out in favor of clips. They keyboard now makes more sense. It's now a bit easier to move about your squad members. Some mechanics are just as poor as always, and require doing multiple things.
I don't know about buying/selling yet, nor equipment improvement.
There's an over-dramatic story, too.