Jeff Hanneman wrote some of the most unforgettable riffs and was the heart and soul of Slayer. His writing style felt like punk with a hint of thrash and worked so well for that band. And (thanks to Jeff) that riff in "Black Magic" is killer. I always thought it was strange how Kerry King was more popular than Jeff, even though Slayer would not have been one of the Big 4 without Jeff. As a drummer, I was personally obsessed with Dave Lombardo (and still kind of am). I would spend hours when I was a kid learning his double bass parts .
I definitely know what you mean about people randomly chanting Slayer. The band still continues to make an indelible impression on popular culture. I work in hip-hop and a lot of rappers today are even now listening to Slayer.
One more Slayer track that I believe is criminally underrated: