When I listen to Slayer, it makes me wanna scream and headbang. It takes all those feelings away, like anger or disappointment. I feel so well afterward.
Their songs are so powerful they take me by the guts, just an amazing feeling. They just know how to play thrash metal.
Another thing why I'm a big fan of Slayer is the voice of Tom, he keeps it natural. It's not like bands like Cannibal Corpse (nothing against them) where the singer has a roaring voice and you don't understand shit about what he says. Tom screams (hopefully he does) but it remains his natural unique voice.