Agreed with the length and pace. Also, it seemed like there was at least one bit that was edited, somewhat near the beginning. The music is nice, but just watching hands (that frequently go nearly out of frame) fiddle with cards for over three and a half minutes is boring. I'll be honest, I only stuck it out to the end to see if I could catch any more glitchy bits that looked like edits.
What Goatears was saying is right. Too much shuffling becomes counter productive. Not only does it lead people to just assume something else is going on, but if they get bored they won't bother finishing the video. One or two 'solid' shuffles should do it. Maybe three or four, if you've already shown that you have prowess with cards. Like Ricky Jay's gambling demonstration in Ricky Jay and his 52 Assistants, "Watch as I do what should be good solid riffle shuffles.."
I don't think a script is necessary, unless you want to shuffle for three minutes and twenty seconds. I don't know what you should say, it's your job to make me want to watch to the end of the video. Make it interesting.
Out of curiosity, what is the experiment? What are you trying to figure out?