This applies to both the PS4 and the XBOX One: the x86 architecture. It means less cost that developers have to absorb to bring titles out on PC, PS4, and XBOX One, meaning more competition in the marketplace, which ultimately means (hopefully) lower prices on quality entertainment.
Next is probably the HDMI input. That's the most disruptive thing to happen this generation. It's simple, but it has so much potential.
Then the focus on making the app switching quick, and the instant on feature (if that makes it to final release).
Beyond that I suppose the games will be great, but they really seem to be lagging as far as Indy games are concerned. The XBOX team needs a dose of Balmer's famous "DEVELOPERS DEVELOPERS DEVELOPERS DEVELOPERS" pep talk.