I got a chance to play a bit of D3 over the weekend, and had a very good time running public games.
For starters, you get and extra 10 percent XP and MF for each other player in the game up to 30 percent. Also, because it was the one year anniversary of D3, you get an additional 25 percent boost until tomorrow!
The first incredible addition is that they actually added monsters to the other acts. I ran Act 1 a few times and there are now GOBS of monsters. Each run netted me about 4-5 bars of XP. I went from Paragon 55 to nearly Paragon 57 in just about 3-4 runs.
I also grabbed a couple of Legendaries. They were not very good, but it is nice to see that shiny orange stream of light.
Another nice addition is the Tome of Cain that lets you identify all of your rare's in one shot instead of constantly clicking each one to ID it.
Overall, it think it was a pretty good patch.