I took Hysteria because I needed the points to advance, but I am not sure how I feel about it. The buff is quite nice, but it's also quite risky. I have bit the bullet a couple of times when popping it, meaning my self heals would not keep up with the damage I was taking. Maybe if I hit it off with Mark of Blood at the same time.
I'm personally liking playing a DK because it is a sharp contrast to my Balance Druid and I actually enjoy it more than my Rogue, whom I haven't touched since the expansion came out. Poor girl is sitting down resting somewhere in the Hinterlands right now, wondering when I'll level her to 49.
Yet to try the Frost spec or Unholy for my DK, but am tempted.