Some of the weapon perks talk about a chance to do critical damage, or double critical damage. Is this something seperate from a finishing move?

Does a finishing move actually do extra damage? What I mean is, it seems like it kills the target, ignoring health altogether (which, if the target had a bunch of health, might mean that effecitvely, it did more damage than the attack otherwise would have)? Or, is a finishing move just when the game detects that your current attack would do so much damage that the target is dieing anyhow, and it just occasionally plays an extra animation for the deathblow?

Finally, are finishing moves completely random, or is it based on how you attack the enemy, like combinations of attacks like standing-power,quick slash, sideways slashing power. That is, can I through some level of skill, trigger finishing moves against tough opponents?

I believe the deathblow animation simply recognizes that your attack is powerful enough to kill the target off, whether it was a power/critical attack or normal. I see deathblow animations a lot while killing wolves, and i can kill them with one normal swing.