There's a ton of changes, I go back to it after taking a break for a month usually and I'm always pretty amazed by how much stuff they added in/changed around.
Can't speak much for endgame but there's a crap load of new raids and instant adventures makes endgame raiding a lot easier/more fun. Ember isle is something I haven't been to but I hear it's good as well.
Hey, I just started playing Rift today. I guess there's currently a christmas event going on and I'll be sure to let you know how it's doing once the servers come back up. The patch notes said something about a new update and stuff for players level 40+, so maybe that's what you were wanting? I guess it's called instant adventure or something.