I was originally very skeptical of this skill... as a Warrior it costs me about 70 health to cast, and I'm only going to get 9 back on any strike.
Order of the Vampire isn't a healing spell. It's an offensive boost. Think of it as "For 5 seconds, all of your parties physical attacks do +9 damage. Oh, and there's some minor healing." Or +4, or +13, or whatever your skill puts it at.
Looking at it this way, I can afford to pay 70 health for something like this. I used it with great sucess taking out the 22 level Sand Wurms. (And if you care about health economics, for me each strike is a net gain of 18 health for my party. We only need to make 4 such strikes for the Order to pay off.)
I captured mine off the third Forgotten leader in the Thirsty river Mission. There's quite a few elites on them in that mission.
Does the effect work on minions too? If it does work think about the destruction spamming Order of Vampire/Pain with an army of Bone Minions out can do. Then Taste of Death when you get low
In my opinion, with a party of 8, this skill is absolutely devastating during a heated battle. Against high level people, it can nearly double total party damage for 5 seconds, and with quick attacking party it’s awesome. It’s like Order of Pain and Vigorous Spirit (for every member) for five seconds all packaged into one little sacrifice skill.