The biggest difference between Slashdot and Hacker News is that I find Slashdot to be much more accepting of humor. There is plenty of good discussion there, but there are also plenty of quality one liners and inside jokes, both of which seem to be lacking on hacker news. It's like two newspapers, but one has a comics section. That said, I think /. is an older crowd, and I got there late to the party, Hacker News is more my generation I suppose.
I find Slashdot to be completely lacking in humor. It used to be different back before they cracked down on the trolls, but these days it's about as bland and humorless as you can get.
