One of the big questions about next-generation consoles is how
much of a difference they'll make when it comes to cross-
generation titles. In the case of Assassin's Creed IV: Black
Flag, the difference is purely in the visual department
according to associate producer Sylvain Trottier.  "For us, it
was a fundamental law: this is the same game, no matter what the
platform," Trottier tells The Verge. He explains some of the
tricks and techniques that make the PlayStation 4 and Xbox One
versions look better, like more realistic environments.
Development for the new hardware did improve the current
generation versions. For instance, plants don't move as
naturally on older consoles, but they are better for the tech
incorporated into the Xbox One and PS4 iterations. You can read
more about the visual differences in The Verge's interview. If
you're trying to decide between the PlayStation 4 and Xbox One
versions, know that the exclusive Sony content will later be
available on other platforms.  [Source: The Verge]