I'm on an XB1 Elite, fittingly, and since the most recent patch everything's fine so far.
The most recent main update absolutely killshotted a lot of people's fps... me included, but that got fixed swiftly, and I think maybe it's as smooth as it's ever been? Or at least equal to its past best.
Re how much has changed; that kinda depends on what you care most about. The new mining system's fun (and pays well), and the game at long, long last got some actual exploration mechanics... I'm an anti-social role-playing bar-steward, so you'd have to ask others about PvP. ; -) The Codex, Pilot's Handbook, and voiced Galnet feed are all fine additions, but some may completely ignore them, so those are very subjective.
The game now feels a little more lively in terms of signal sources, mission triggers, new installations, and so on.
I personally can't find any other conclusion than it's easily the best it's ever been, but I am always a glass half full kinda guy when it comes to this game.