How odd. For me Unholy is completely easy and intuitive, but tanking and DPS. I personally had issues with working a Frost rotation and I had threat issues in blood which I'm sure was due to unfamiliarity with it.
Unholy's rotation is thus:
BB->SS->SS->BB(I think that's how rune cd work out)
Funny thing is, that's for both DPS and tanking. You only need to add in the occasional HoW if you don't have the RP for UB due to RS :P