I totally agree with you.
Well, While certainly the effects such as the echo are a lot better in the 2nd video, the voice itself is not as deep and creepy as in the 1st one. The 1st video reminded me a lot more of SC1's Zeratul voice. The 2nd voice, in spite of having better sound effects is just too different. I would rather have the voice actor that did the 1'st video but with the improved sound effects the 2nd video had.
Also about visual effects... the 2nd video is obviously better in most aspects, but I didn't like how they diminished Zeratul's eyes glow, it looked better in the 1'st one with that psionic effect that reminded archon's eyes.
in the 2nd video, it's just a round green glow without the gas styled psionic emanations... too bad so sad... why did they do such a thing?
Also, the dialogues and story context of the video changed... that sounds quite interesting...