If it's all in-game I think they'll all say it's great.
In my view, the most powerful idea behind the multi-layer animation system is NaughtyDog's attention to details. As long as they retain this trait, the technique will continue to improve and differentiate with each revision -- even if there are short falls in the first implementation. People will generally pick out (other) things they don't like. So I'm not sure if they will all say "great" if the blending is all in-game.
Whether the idea turns out well depends ultimately on whether the control feels responsiveness, and whether the animation looks natural enough (and has weight). It is somewhat irrelevant if it's 80% in-game or 20% cutscene or vice versa. I am sure ND will make the best decision to ensure a quality experience whatever their project constraints are.
So far from the trailers, it
looks like what we have seen are predominantly in-game. We'll get to play it soon anyway.
I'm more impressed by animation that's reactionary to physics.
Not sure if it's in Uncharted. As it stands, it already has tons of things going.
e.g, common object physics, very nice water, solid fireball, blended animation, swaying/moving plants, animals, wet/damp effects on clothes, wrinkles, facial expressions, mouth animation, eyeball movement, muscle emulation, a rather lively story and cutscenes as opposed to stiff ones, etc.). Again, we will know for sure in a matter of days/weeks.