Remember when you entered a public cowrun game in Diablo 2, entered the portal and found yourself in the middle of cows and dead quarter of a second later?
Well, it's back, so to speak, and it's uglier than before. Some people are luring elite packs to town, making the game public, and when other people join = they're dead before they know what's happening. I have a friend of a friend in real life that I talked to yesterday, that confirmed killing over 50 HC characters this way, mostly in Hell / Inferno.
So keep your eyes open and escape skills ready when entering public games.. if you enter them at all.