Well, I'm not sure the last time RZ played, but if it was before Nightfall, the heroes alone are a fairly big change. As far as updates go, soul reaping for necromancers got a fairly large nerf, only works every 5 seconds now. Ritualists are dominating PvP. Theres the new "hard mode" which makes everything lvl 20+ and is supposed to have better loot. There are now lockpicks which are essentially keys that cost 1.5k and have a chance to be used more than once (which increases with certain titles you can earn). Armor from prophecies and factions got upgraded to the insignia system so now you really can have any armor look with any stats. Um.. theres now this thing called loot scaling which makes gold (as in money) and white items drop less for every person under 8 in the party; aka, a nerf to solo farming.
Lets see, some other good stuff, you can now get scrolls that teleport you into the Fissure of Woe, the Underworld, The Deep, and Urgoz's Warren regardless of which region has favor or who controls Cavalon/House Zu Heltzer. Scrolls to Deep/Urgoz take 1000 faction of the corresponding faction (which is one winning alliance battle, 2 if you lose both times) and UW/FoW scrolls drop in hardmode. Hmmm... they added an official wiki that you can access by pushing F10 or typing /help. Oh, theres an automated tournament system now so you can sign up and play in the PvP tournament without having to set up matches.
They've also added some little stuff here and there like specific weapon sound effects for axe/sword/hammer hitting various materials...
Some of the update stuff is cool but a lot of it is just polishing making the game more solid.