I saw a dual wield finisher in 1st person.
There are different finishing moves for each weapon and each kind of enemy. What you saw was a sword finishing move for a human being. However, we saw two other finishing moves for a wolf (sword) and a dragon (battle-axe) in the demo... of which both forced the player into third person. One was also in slow motion.
I dislike slow motion and it feels kinda lame and more suitable for a blockbuster movie... but I can live with it. What I truly hate though is how finishing moves sometimes force you into third person. Totally breaks my immersion and "feel of combat".
I won't play Skyrim with it unless I can find a way to disable it, either through a gameplay setting or a mod.