Looks like there are some major changes to unholy DKs:

• Death Knights had a lot of balance changes over time. They had unique
  mechanics, like DoT snapshotting with Unholy. Those things have gone
  away now, so part of what made Unholy special is gone.
• Something they are trying now is Festering Wounds. When the Death Knight
  hits a target, they will apply debuff and when they use a different
  ability that wound will pop. You might hit them and apply three or five,
  or pop three of them all at once.
• The fantasy of a Death Knight pulling corpses from the ground to do
  their bidding is great, but in the game it doesn’t feel like that when
  you are playing, so the team wanted to give them a unique mechanic.
• Talents may give them multiple pets, different pets, stronger pets.
• Frost is still very similar to live and Blood is somewhere in the middle.
• Blood Death Knights having the different rune types is part of what made
  it easy to play. You would just push whatever buttons were lit up, as
  the runes controlled what you could use. Now you will have more options
  and control over how to use your runes.