Sure that sort of thing is pretty impressive and many players would think "that's cool, that I can do that in game." But really, does it all need to be pointed it out?
First of all, the voice over seems a bit contrived. Who is this developer and when did he develop his movie-trailer voice? Plus, a lot of the action taking place is in fact... kind of slow. That's probably when the voice over talks the viewer through some of the action and sells it in a good way. When Ezio is impeded by the gate and has to find an alternate path, I have to admit that it seems like the same gameplay we were met with in Assassin's Creed (one). Instead, the developer voice over insists that this is a good thing. "Players will have to react quickly... blah blah blah."
Look, it's bull shit. I'm convinced, I'm going to buy Assassin's Creed II at some point, but please don't baby talk me through some gameplay footage. It makes me feel like I can't really trust it, like it needs to be verbally inflated in order for me to keep my interest up.
I hope to God AC II turns out to be a better game. I enjoyed AC (one), but in the end I put the game down half way through and finished it six months later. I don't want to have to do that again just to enjoy the game thoroughly, and without burnout. We'll find out soon enough as Assassin's Creed II is released in November.