They do not happen everytime for me, so to me it is very satisfying when i defeat a enemy and the kill move kicks in. :drool:
Well you could try this mod when you dislike them then.
http://www.skyrimnexus.com/downloads/file.php?id=33
Unfortunately I play on xbox

Still, that link is useful for pc players who want to turn them off

Edit, to poster above:
Well.. What I dont like is that its often pantomime swordplay. You know, where they plant a sword under your arm and then the 5 min death scene starts.
The weapon hits beside the target, next to the NPC entirely, doesnt connect.