We haven't seen Uncharted 4 gameplay yet. The trailer they released was not gameplay. It was, however, the in-engine cutscene graphics displayed in real time output by the PS4.
I'm sure most of us have played The Last of Us. It had pre-rendered cutscenes (which in this context basically means its just a video), it had real-time cutscenes (graphics being rendered by the console; same as the U4 trailer), and then of course, it had gameplay. Most people playing through that game probably couldn't tell the difference between the prerendered cutscene graphics, the realtime cutscene graphics, and the gameplay graphics. The pre-rendered cutscenes DO look better, there's more post effects on them, higher AA and the like, and higher quality models. The other two are essentially the same graphics, one is simply playable and the other is not. They can push more eye candy onto the screen during the realtime cutscenes on the models for close-ups and other things if they choose to, but they're both 100% off the hardware, and Naughty Dog is exceptional at keeping them 1:1.
This is a real-time cutscene, and this is Naughty Dog, so it should be representative of what we're gonna get from the gameplay.