Its heavier on Skyward Sword than any other, but its got enough of every other game to be worthwhile. Alot of it depends how much concept art and story exists for the game.
Games with huge character design changes like Ocarina of Time, Wind Waker, Twilight Princess (wolf-form and Midna) are well represented in the art section, while games that don't, like Majora's Mask, only get a few pages. The more recent games have more art as well: only a few pages of concept art for Legend of Zelda and Adventure of Link exist, but there's pages and pages for Skyword Sword, Phantom Hourglass, and Spirit Tracks. Its fascinating to read the developer notes on alot of the art, or see what characters might have looked like had the design team gone a different way (imagine what path the series would have taken had Zelda worn a sci-fi space hunter outfit instead.)
Games that have greater impact on the three timelines also get more pages of the history/story devoted to them. Skyward Sword gets a good bit for being the beginning of the story, Ocarina of Time gets the most for being the branching point of the three timelines, Four Swords gets a lot for introducing Vaati, and the whole Wind Waker-Phantom Hourglass-Spirit Tracks arc gets alot since its the most flushed out of the three alternate history branches (probably becuase its the most recently developed.) Games that are viewed as having less impact on the overall story (like Link's Awakening) get less history devoted to them.
The last 20 or 30 pages are the first chapter of some 10 chapter Skyword Sword manga, so this makes people think thats its a Skyword Sword book, even though its not.
Now what exactly do you mean by "Don't want to spoil myself yet"? Have you not played through Skyword Sword yet!? WTF are you waiting on??