Slayer crowds now compared to how they were when I first started going to shows are more of a controlled crazy. They'll mosh, have a good time, scream the lyrics, maybe even drink one too many beers, but not get too out of hand.
Back in the day it was complete chaos. Fights, drunk people vomiting in the pit, throwing shit on stage, leaping off balconies, wrecking the bathroom, booing opening bands off the stage. It was kind of fun to see, but annoying if it got too close to you and impacted your enjoyment of the show.
I'm probably just getting old, but I prefer watching Slayer today and not worrying as much about getting puked on or punched in the back of the head by some drunk skinhead who thinks he's moshing.