It's nice to see a developer be relatively transparent when it comes to technical specs of the many versions of a cross-generation game they are working on. Hideo Kojima lived up to his promise and provided details on what fans can expect from the PS4, Xbox One, PS3 and Xbox 360 versions of Metal Gear Solid: Ground Zeroes (and presumably The Phantom Pain) prior to launch.
As expected at this point with multiplatform releases, the PS4 version is pushing the most pixels, with the Xbox One a bit behind, and the Xbox 360 and PS3 falling behind by varying degrees. The big difference between the next-gen versions of Ground Zeroes boils down to the resolution at this point. The PS4 will render the game at a "full HD" 1080p (1920×1080) resolution , and the XB1 with a more last-generation standard 720p (1280×720). Both are targeting 60fps in terms of framerate.
The PS3 and Xbox 360 version are shooting for "internally scaled" 720p, which probably means they are rendering at below 720p natively and being upscaled to 720p. Both of those versions are targeting 30fps as a framerate. Based on screenshots alone, the game looks more than competent on all platforms at this point to be honest
Take a look at KojiPro's chart along with some comparison screens for ideas on what to expect.
PS3 vs PS4
Xbox 360 vs Xbox One
Current generation machine version / next-generation version comparison table (resolution and number of frames)
PlayStation 3 PlayStation 4 Xbox 360 Xbox One Resolution 720P (scaling internally) 1080P 720P (scaling internally) 720P Number of frames 30fps 60fps 30fps 60fps