Well, like others have said the difference between the PS3 and the Xbox 360.
But it is a little more complected than just the GPU and the other hardware differences. The Xbox One will use DirectX 11.2 (something) the PS4 will use OpenGL (and/or possible license a DirectX 11 from Microsoft) OpenGL used to be the better platform, but in my opinion since around DirectX 6, the DX version has been better. (The original Xbox is DirectX 8, the X360 DX is 9C.)
The later Uncharted's look great, but so does Halo 4. They are both pushing those great graphics on the older systems. (I am looking forward to Halo 5 at 60fps.)
Visually, I think we will have things similar to this gen, where we have a visibly noticeable less powerful WiiU and the visibly about the same 1080P HD Twins.
As far as PC's, they sort of have their own generation. Yes, we get better hardware - more goddies, better frame rates, etc. but that's trimmings. We will probably not see huge increases until DirectX 12, which is probably not coming out till Windows 9. Which is probably at least a few years away.