Not much at launch. Both systems are way stronger than devs can handle and they are running cross gen games. Should be stuff only tech experts notice.
At the end of the gen though, it will be huge. As devs squeeze every ounce of power out of both systems, PS4 games could look much better than the xbox versions. Think og xbox verse ps2, but flipped and a bigger difference.
PS4 exclusives will be what really shine though.