It can be good, as long as the finishing moves:
1) AREN'T in slow-motion.
2) DOESN'T force you to go into some kind of automatic V.A.T.S (like in third-person) while you do it.
If one of these above features are implemented, I probably won't buy the game until there's a mod that gets rid of it. I would hate it that much
Edit: What I would want is something like... hm. Something like, when the enemy is down on the ground, you can do this finishing move, and thrust the weapon deep into his/her chest, killing instantly. All done in 1st person (or 3rd person if you're using that) and in real-time.
Yeah, like you swing the sword to the side in one big sweep as you would during combat and chop a guy's head off. He'd have fallen down on his knees at this point so he'd be right in line for it. Or jab him in the chest.
This brings up an alternative option though. If we beat our opponents into submission, then can we simply walk away without killing them? Now that would be an interesting finisher. Especially if you bumped into them limping around on the street days later in bandages. How awkward would that be?
you: Oh, uh, hey.
bandit: Oh, i uh didn't see you there.
you: yeah, well i had my cloaking spell on.
bandit: yeah... *cough*
...
you: so how's the sword gash?
bandit: i uh... lost a thumb.
you: ah...
...
you: well i better be off.