I've seen the destroy and control endings so far. They both definitely improve on what we had before, and the control ending has some particularly cool dialogue.
The Starchild has some extra investigation dialogue options which is nice, and I'm pretty sure the wording of some of his lines have been changed to include slightly better wording. There's also a new ending that's been added.
You can see that if you decide to shoot the kid.
There have been a couple of minor changes such as
the Mass Relays no longer being destroyed in any of the endings
but the rest is just additional scenes. I still don't think it's worth downloading but it's definitely a must-watch for anyone that's played the game.