Edit: This post is primarily for PvP'ing with Frost and Unholy
So I've put a lot of thought into how to improve frost and unholy DK survivability without making them over the top.
Right now, DS heals you 20% of the damage sustained in the last 5 seconds (minimum of 7%). So basically, DS heals you for 7%, assuming I read the tool tip right. What I propose is that DS heals you for 7% PLUS 20% of the damage sustained in the last 5 seconds, at which point, when the 5 seconds are up, you get the extra 20% of the damage back. The catch is, if you DS before the 5 seconds are up, you reset the 5 seconds. That way, you can't keep spamming it, or you pay a huge rune cost (unholy + frost), for a small amount of health back.
If you Imagine an enemy taking 20% of your health in 5 seconds, during a burst, you will get .2 x .2 = .04 health x total health. (basically 4% plus the 7% base) . That's 11%, much more manageable than the 15% for every death strike we received when we spammed DS with glyph of dark succor.
If you had somebody take 50% of your health off in 5 seconds (which would be horribly bad), you'd get 10% + the base 7% = 17% which I don't think is too much to ask for, considering that you'd have to have half your health lost in 5 seconds to get that amount back.
People's thoughts?